Definitions and Line Drawings
of Botanical
Terminology
Below are brief definitions of the botanical terminology that may be encountered at this website. Some botanical terms are illustrated by line drawings. Many of these line drawings have been reprinted electronically by permission of the publisher, Iowa State Press. They originally appeared in Kansas Prairie Wildflowers (1980) by Clinton E. Owensby.
Achenes – A dry non-fleshy fruit containing a seed; the coat of this fruit is somewhat hard. Such seeds are typical of the Asteraceae (Aster family) and other plant families.
Alternate – The leaves are arranged alternately along the stems of a plant. This is a common arrangement. See line drawing of Alternate leaves.
Annual – A plant that completes its life cycle in less than one year. Some plants are summer annuals that germinate during the spring or early summer and mature by the fall of the same year; other plants are winter annuals that germinate during the fall and mature during the spring or summer of the following year.
Anthers – Anthers bear the pollen of the flowers; they are located at the tip of the stamens (male reproductive organs). The anthers of a flower are often powdery yellow or orange in appearance (from the grains of pollen) and each anther is usually oblongoid in shape.
Appressed Hairs – Refers to hairs that lie flat against the stem or the surface of leaves.
Astringent – Foliage with a soapy or medicinal aroma because of the presence of saponins and other chemicals.
Awn – This refers to a needle-like bristle at the tip of a floral scale in grasses, sedges, and other plants.
Axil of a Leaf – Where the stem of a leaf (the petiole) joins the stem; this is where a side stem or flowering stalk may develop.
Basal Leaf – A leaf that develops from the rootstalk, rather than a stem.
Beak – This is a pointed slender appendage that defines the outer tip of a seedpod; the seedpods of many plant species lack beaks. For Carex spp. (Sedges), this term has a different meaning. The perigynium of a Carex sp. can have a slender beak at its apex to enclose the long style of a female floret, or the perigynium can be nearly beakless when the style of the female floret is quite short.
Biennial – A plant that requires two years to complete its life cycle. During the first year, a biennial typically consists of a rosette of basal leaves, while during the second year it bolts and develops one or more flowering stalks.
Bifurcated – A structure that is divided into two parts along some portion of its length. This often refers to petals that are deeply notched at their tips, as occurs in the flowers of Stellaria spp. (Chickweeds) and Cerastium spp. (Mouse-Eared Chickweed).
Bipinnate Leaf – A compound leaf with pairs of side stems arranged oppositely along its central stem (petiolule). On each side stem are pairs of leaflets that are arranged oppositely from each other. Also, the central stem usually terminates in pairs of opposite leaflets. Terminal leaflets may, or may not, be present. See line drawing of Bipinnate Leaf.
Bipinnatifid – A simple leaf or leaflet that is pinnatifid with lobes along its side margins; these lobes are also pinnatifid with secondary lobes along their margins. Some species of ferns have bipinnatifid leaves; the lobes of such leaves are often cleft.
Blade – This the extension of the leaf that spreads away from the stem (or culm). Most plants have leaf blades, although Eleocharis spp. (Spike Rushes) are an exception. The 'leaf' of a forb usually refers to its blade. In contrast, grasses, sedges, and some forbs have an extension of the leaf that wraps around the stem (or culm) of a plant. This is the 'sheath' of a leaf.
Bracts - Bracts appear at the base of an inflorescence; they often resemble narrow leaves. While most bracts are simple, they are sometimes divided into branching lobes. Many species of plants in different families have bracts; for some species in the Apiaceae (Carrot family), bracts occur at the base of an umbel or a compound umbel.
Bractlets – Small secondary bracts that may appear near the flowers of an inflorescence. They often resemble small linear leaves, but some of them are stiff and spine-like. Some species in the Apiaceae (Carrot family) have bractlets underneath their umbellets.
Branchlets – This refers to the side stems that develop from the central stem of some Equisetum spp. (Horsetails). Sometimes these side stems (or branchlets) divide into secondary side stems (or secondary branchlets). For some species of the Apiaceae (Carrot family), this term refers to the stalks underneath the umbellets in a compound umbel of flowers.
Bulb – This is a short underground stem that is enlarged by modified, fleshy leaves. These modified leaves contain no chlorophyll and are appressed together; they store nutrients and water for rapid growth and development during the spring. A bulb is spheroid in shape, with short coarse roots radiating from the bottom. See line drawing of a Bulb.
Bulbets – Small bulbs that are produced underground or above ground as an alternative to seeds. Above ground bulbs are produced in the inflorescence and are called "aerial bulbets." Such bulbets are often produced by some Allium spp. (Onions).
Bulrushes – A common name that refers to species in the genus Scirpus. Because Scirpus spp. (Bulrushes) are members of the Cyperaceae (Sedge family), they are actually sedges, notwithstanding the common name.
C3 Metabolism – Cool-season plants use a C3 metabolism to convert sunlight into carbohydrates using chlorophyll. They often grow best during the spring or fall when the weather is cool and moist. Most forbs and some grasses and sedges have a C3 metabolism. The chemical pathway of C3 metabolism is slightly different from that of C4 metabolism (see the description below).
C4 Metabolism – Warm-season plants use a C4 metabolism to convert sunlight into carbohydrates using chlorophyll. These plants often grow best during the summer when the weather is warm and somewhat dry. Some grasses and most Cyperus spp. (Flat Sedges) have a C4 metabolism. The chemical pathway of C4 metabolism is slightly different from that of C3 metabolism (see the description above).
Calyx – The part of the flower underneath or behind the corolla that consists of sepals; sometimes the sepals are united to form a tubular calyx with teeth along its outer rim. The calyx is often green, but can assume other colors.
Canescent – The surface of a leaf or stem that is densely covered with hairs that are very fine and very short; the surface is finely pubescent.
Caudex – This is a spheroid enlargement at the base of a plant that is usually below the surface of the soil (in herbaceous plants). A caudex is woody and functions as a storage organ for nutrients and water. One or more stems develop from the top of a caudex, while coarse roots radiate below. See line drawing of a Caudex.
Cauline – This refers to the leaves along a stem (or culm), as opposed to leaves that develop directly from a rootstock in the ground (i.e., basal leaves). Cauline leaves occur in pairs (opposite), alternately, or in whorls along the stem.
Central Axis – This expression usually refers to the central stalk of an inflorescence that is a spike, raceme, or panicle. Sometimes it refers to the central stalk (or rachis) of a compound leaf.
Ciliate – There are fine hairs along the leaf margin. A ciliate margin is often smooth (entire) as well. See line drawing of Ciliate margin (Copyright © 1980 by Iowa State Press).
Cleft – The leaf is sharply divided into lobes; it may be pinnately or palmately cleft. The ends of the lobes are often pointed, rather than rounded. See line drawing of Cleft shape.
Composite Flower – A flowerhead consisting of numerous small florets. This flowerhead may have ray florets (a small flower resembling a petal) and/or disk florets (a small tubular flower with tiny lobes). The florets are held together by floral bracts surrounding the base of the flower.
Compound Umbel – A cluster of flowers in which the flowering stems originate from the same central location; each of these stems terminates in an umbellet of flowers. See line drawing of Compound Umbel.
Cones – This refers to the spore-bearing structures of Equisetum spp. (Horsetails). These cone-like structures occur at the apex of the central stems. They resemble pine cones in shape.
Cordate – The leaf is rather wide and heart-shaped (but upside-down). The broad base of the leaf curves upward toward the end of the petiole (leaf stem), while the apex narrows to a point. See line drawing of Cordate shape (Copyright © 1980 by Iowa State Press).
Corm – A corm is similar to a bulb (see above), except the modified underground leaves are usually woody and scaly. Occasionally, the spheroid surface of a corm is irregular and contains ridges. Coarse roots radiate below. See line drawing of a Corm.
Corolla – The often colorful part of the flower above the calyx consisting of petals; sometimes the petals are united into a floral tube that has spreading lobes along its outer rim.
Corymb – Similar to a raceme, except that the flower cluster is flat at the top; the outer flowers usually open first. The pedicels of the outer flowers are longer than the inner flowers. See line drawing of Corymb (Copyright © 1980 by Iowa State Press).
Crenate – The leaf has blunt teeth with convex sides; the indentations between teeth are somewhat angular, rather than rounded. See line drawing of Crenate margin.
Culm – The central stem of grasses and sedges. This stem is usually unbranched and it terminates in an inflorescence. The culm is often largely hidden by the sheaths of the leaves, which wrap around it.
Cyathium – A cup-like structure that contains the male & female flowers of the Euphorbiaceae (Spurges). There are often petal-like appendages along the upper rim of this cup-like structure, and there is often a gland at the base of each appendage.
Decurrent – The lower portion of a leaf that lies flat against the stem; Verbascum thapsus (Great Mullein) and Cirsium vulgare (Bull Thistle) have such leaves.
Deltoid – A triangular-shaped structure of a plant; this term often refers to the shape of a leaf blade.
Dentate – The leaf has widely spaced teeth that are pointed at their tips, but with concave spaces between them; this dentation can be irregular. See line drawing of Dentate margin (Copyright © 1980 by Iowa State Press).
Dioecious – Plant species that produce either all female flowers or all male flowers, but not both on the same plant. The Thalictrum spp. (Meadow Rues) are examples of dioecious species.
Disarticulation – As the spikelets of grasses become mature, their floral scales (whether glumes and/or lemmas) become separated from their stems and fall to the ground. When the glumes (the lowermost scales) persist on their stems while the lemmas fall to the ground, this is referred to as 'disarticulation above the glumes.' When both glumes and lemmas separate from their stems and fall to the ground, this is referred to as 'disarticulation below the glumes.'
Doubly Serrate – The leaf margin has smaller teeth interspersed between larger teeth. See line drawing of Doubly Serrate Margin (Copyright © 1980 by Iowa State Press).
Drupe (compound) – A compound fleshy fruit consisting of numerous drupelets. Each fleshy drupelet has a single seed with a hard covering. Raspberries, blackberries, and dewberries are examples of compound drupes.
Drupe (simple) – A fleshy fruit containing a single large seed with a hard covering. Cherries and plums are examples of simple drupes.
Ellipsoid – Refers to a slightly flattened 3-dimensional structure that is more broad toward the middle than at its two outermost edges. For example, a seed can have an ellipsoid shape. The 2-dimensional counterpart of ellipsoid is the term 'elliptic.'
Elliptic – A 2-dimensional curvilinear structure that is more broad toward the middle than at its two outer edges. An elliptic leaf has the same shape as an ovate leaf, except it is more narrow.
Evenly Pinnate Leaf – A compound leaf with pairs of leaflets arranged oppositely along its central stem (petiolule), but without a terminal leaflet. There is always an even number of leaflets. See line drawing of an Evenly Pinnate Leaf (Copyright © 1980 by Iowa State Press).
Fibrous – The root system consists of a loose collection of more or less thin branching roots that originate from the base of the plant. See line drawing of Fibrous root system.
Filament – A long thread-like structure with an anther at its tip; the filament connects the anther to the base of the flower. Each flower has several filaments with anthers at their tips.
Flat Sedges – This expression refers to species in the genus Cyperus. As one would expect, they are members of the Cyperaceae (Sedge family).
Fleshy – A fleshy root is a central taproot that can be nearly as wide as it is long. This is a very stout taproot that is sometimes incorrectly described as "tuberous." See line drawing of a Fleshy taproot (Copyright © 1980 by Iowa State Press). Sometimes fibrous roots are described as "fleshy." This means that they are somewhat thicker than ordinary fibrous roots, and they have a softer texture.
Floral Bracts – A compound flower often has floral bracts that circumscribe its base, particularly among members of the Asteraceae (Aster family). These scale-like bracts surround the ovaries of the flower and they are often appressed together. They are often referred to as 'involucral bracts' or 'phyllaries' by botanical authorities.
Floret – A small flower that lacks sepals and petals. This often refers to the flowers of grasses and sedges and other wind-pollinated species. For plants in the Asteraceae (Aster family), this refers to the disk florets and/or ray florets of a flowerhead (a compound flower). A ray floret has a petal-like appendage to which is attached the reproductive organs of the floret; the ray florets of some species are sterile. A disk floret consists of a tiny tubular corolla and the reproductive organs of the floret; sometimes the disk florets are sterile as well.
Flowerhead – A crowded cluster of stemless or nearly stemless flowers; these flowers are either disk florets or ray florets. The shape of the flowerhead can be convex or rather flat. See line drawing of Flowerhead.
Follicle – A seedpod that splits along one side to release the seeds; Milkweeds and other plant species produce such seedpods.
Forbs – These are plants that produce flowers with conspicuous petals and/or sepals; the flowers of such plants are often showy and insect-pollinated. In contrast, grasses (Poaceae), sedges (Cyperaceae), and miscellaneous other plants are not forbs because their wind-pollinated flowers lack petals and sepals, or their petals and sepals are tiny and inconspicuous. Such wind-pollinated flowers are not very showy, although there are some exceptions.
Fruit – This is a very broad botanical term that refers to the seeds and their surrounding covering; a seed may be contained with a papery membrane, hard coat, fleshy pulp, spongy pod, or other structures.
Funnelform – A corolla that is shaped like a funnel, being narrow and tubular at the base, but flaring outward toward the outer margin. The corollas of Ipomoea spp. (Morning Glories) and Calystegia spp. (Bindweeds) are funnelform.
Glabrous – The surface of a stem or leaf that is smooth and hairless.
Glaucous – The surface of a stem or leaf that is smooth with a white bloom that can be rubbed off.
Globoid – A 3-dimensional structure that is shaped like a globe or sphere. For example, a seed can have a globoid shape. The terms 'globoid' and 'spheroid' have the same meaning. The 2-dimensional counterpart of a globoid shape is a shape that is circular, round, or orbicular.
Glume – A glume is one of the lowermost scales in a spikelet of grass; each spikelet of grass has a pair of glumes at the bottom. The glumes are usually keeled and somewhat flattened; they are infertile and don't contain any florets. The 1st glume may be very similar in size and shape to the 2nd glume, or they may be quite different in appearance from each other. The tips of the glumes are sometimes awned. Here is a line drawing of a Pair of Glumes (Copyright © 2006 by Diana Smailus).
Grain – A grain is a seed with a hard coat. It typically refers to the seeds of grasses (Poaceae). Sometimes this term refers to a particle of pollen (e.g., a grain of pollen).
Grass – Members of the Poaceae (Grass family) are true grasses.
Gynecandrous – This refers to a spikelet that has pistillate (female) flowers above the staminate (male) flowers. Some sedges (e.g., Carex spp.) have this arrangement of flowers on the same spikelet.
Hoods – Erect columnar structures on the upper part of a Milkweed flower in the Asclepiadaceae.
Horn – A slender horn-like structure inside or adjacent to the hood of a Milkweed flower in the Asclepiadaceae. The horns are straight or curved, and usually shorter than the hoods. The flowers of some Milkweed species lack horns.
Indusium – The sorus (or spore-bearing structure) of some ferns is partially covered by a pale membrane that is called an 'indusium.' The indusium may fade away as the fertile leaf of a fern matures. The plural form of this term is 'indusia.'
Joints – The central stems and branchlets of Equisetum spp. (Horsetails) consist of several stem-like joints that are connected together at their ends by ring-like sheaths.
Lanceolate – The leaf is broader at the base than at the apex (outer tip); the apex is pointed. See line drawing Lanceolate shape (Copyright © 1980 by Iowa State Press).
Leaf Nodes – Where the leaves join the stem; some species of plants (primarily forbs) will develop rootlets at the leaf nodes where a stem touches moist ground.
Leaves (fertile) – For ferns, these are spore-bearing leaves. In most species of ferns, these spores are produced by small sori (spore-bearing structures) on the undersides of the leaf blades. Otherwise, the fertile leaves of such ferns resemble their infertile leaves, except they are usually larger in size than the latter. However, in a few species of ferns, e.g. Onoclea sensibilis (Sensitive Fern), fertile leaves have a very different appearance from infertile leaves. The fertile leaves are branched, brown, and bead-like in appearance. Each 'bead' of a fertile leaf contains a sorus with spores. In still other ferns, e.g. Osmunda regalis (Royal Fern), only a portion of the fertile leaf is branched, brown, and bead-like in appearance. The rest of the fertile leaf has a normal appearance that resembles an infertile leaf.
Leaves (infertile) – For ferns, infertile leaves don't produce spores. They have a conventional fern-like appearance, but are somewhat smaller in size than fertile leaves for some species of fern, e.g. Polystichum acrostichoides (Christmas Fern).
Lemma – A lemma is one of the floral scales in a spikelet of grass; the lemmas are located above the glumes. Lemmas usually occur in pairs in each spikelet, although sometimes they occur individually. Typically, one lemma in a pair is fertile and contains a floret, while the other lemma is sterile. The lemmas provide some protection for the reproductive organs of the florets and its developing seed (or grain). Like the glumes, the lemmas are often keeled and somewhat flattened. The fertile and infertile lemmas can appear nearly identical to each other, or their appearance may be somewhat different from each other. Sometimes the tips of the lemmas are awned. Here is a line drawing of a Lemma (Copyright © 2006 by Diana Smailus).
Ligule – A structure on the inner side of a leaf at the junction of the sheath and blade. This structure consists of thickened tissue that may contain papery membranes or a row of hairs. The characteristics of a ligule are more observable when the blade of a leaf is pulled away from the culm. Sometimes the ligule is used in the identification of grasses and sedges.
Linear – The leaf is very narrow relative to its length. See line drawing of Linear shape.
Loment – This is a seedpod that is divided into segments; each segment contains a single seed. The shape of a loment is often flattened and oblong; the segments are often more or less rounded. Examples of plant species with loments are the Desmodium spp. (Tick Trefoils).
Monoecious – Plant species that produce both male and female flowers, but not perfect flowers, on the same plant. An example of a monoecious species is Xanthium strumarium (Common Cocklebur).
Node – A node is a small bulge on the culm (or stem) of a grass at the base of a sheath. Sometimes the appearance of the nodes is useful in the identification of a grass species.
Nutlets – Refers to seeds with a very hard coating in some families of plants, including the Lamiaceae (Mint family) and Verbenaceae (Vervain family).
Obcordate – The leaf is rather wide and heart-shaped. The base of the leaf narrows to a point, while the broad apex curves downward in the middle. See line drawing of Obcordate shape (Copyright © 1980 by Iowa State Press).
Oblanceolate – The leaf is broader at the apex than at the base; the apex is rounded. See line drawing of Oblanceolate shape (Copyright © 1980 by Iowa State Press).
Oblique – The base of a leaf is asymmetric; one side of the base is lower than the other.
Oblong – The leaf is somewhat narrow, but rounded on both ends. See line drawing of Oblong shape (Copyright © 1980 by Iowa State Press).
Obovate – The leaf is rather wide and rounded at the apex, but narrows considerably at the base. An obovate leaf is similar to an oblanceolate leaf, but broader. See line drawing of Obovate shape (Copyright © 1980 by Iowa State Press).
Obovoid – Refers to a 3-dimensional structure that is more broad at the top than the bottom. Its 2-dimensional counterpart is the term 'obovate.' For example, a seed may have an obovoid shape.
Ochrea – A membranous sheath that wraps around the stem at the base of a leaf. The Persicaria spp. (Smartweeds) are examples of plants with ochreae.
Oddly Pinnate Leaf – A compound leaf with pairs of leaflets arranged oppositely along its central stem (petiolule), with a single terminal leaflet at the end of this stem. There is always an odd number of leaflets. See line drawing of an Oddly Pinnate Leaf (Copyright © 1980 by Iowa State Press).
Opposite – The leaves are arranged in opposite pairs along the stems of a plant; these pairs of opposite leaves often rotate 90 degrees as they ascend up a stem. See line drawing of Opposite leaves.
Orbicular – The leaf is very wide and nearly round. See line drawing of Orbicular shape (Copyright © 1980 by Iowa State Press).
Oval – The leaf is rather wide and rounded on both ends. See line drawing of Oval shape (Copyright © 1980 by Iowa State Press).
Ovaries – The female reproductive organs of a flower that contain the developing seeds (ovules). An ovary is usually ovoid or globoid in shape with a protective outer wall. The ovary may have a single internal chamber, or it may be divided into several internal chambers.
Ovate – The leaf is rather wide, but narrows to a point at both ends, especially at the apex. See line drawing of Ovate shape (Copyright © 1980 by Iowa State Press).
Ovoid – A seed or seed capsule that is oval or egg-shaped.
Palea – This is a thin inner scale that encloses the developing seed in a spikelet of grass. The palea resembles a fertile lemma (the outer scale), but it is usually smaller and more difficult to observe. Not all species of grass have a palea as a structure in their flowers.
Palmate Leaf – A compound leaf with leaflets originating from the same location at the end of the petiole (leaf stem). It often has 5 leaflets, but may consist of a fewer or greater number of leaflets. See line drawing of a Palmate Leaf (Copyright © 1980 by Iowa State Press).
Palmate Venation – The major veins radiate outward from a central location near the base of the leaf. There are often 5 such veins, but a fewer or greater number is possible. This type of venation is often associated with leaves that are palmately lobed. See line drawing of Palmate venation (Copyright © 1980 by Iowa State Press).
Palmately Lobed – The leaf has lobes that radiate outward from a central location at its base; there are often 5 lobes, although they may be fewer or greater in number. See line drawing of Palmately Lobed shape (Copyright © 1980 by Iowa State Press).
Panicle – A cluster of flowers that branches regularly; each flower usually has its own pedicel (flower stem). A panicle can be narrow and elongated, or rather broad. See line drawing of Panicle (Copyright © 1980 by Iowa State Press).
Parallel – The veins of a leaf are more or less parallel to each other along its length. Leaves with parallel venation are often linear and strap-like. See line drawing of Parallel venation (Copyright © 1980 by Iowa State Press).
Pedicel – The stem of an individual flower. Flowers without pedicels are sessile.
Peduncle – The central stalk of an inflorescence containing one or more flowers.
Perfect Flowers – A flower that contains both male and female reproductive organs. This is the most common type of flower.
Perfoliate – Where the bases of two opposite leaves wrap completely around the stem. It is also possible for the base of an alternate leaf to wrap completely around a stem, but this is less common.
Perennial – A plant that lives for several years, often producing flowers on an annual basis.
Perigynium – This is a bladder-like membrane that encloses the developing achene in the pistillate flowers of Carex spp. (Sedges). The perigynium has a narrow opening at its apex to permit passage of the style. The shape and size of the perigynium is important in the identification of individual Carex spp. (Sedges). The plural form of 'perigynium' is 'perigynia.' Here is a line drawing of a Perigynium (Copyright © 2006 by Diana Smailus).
Petal – a blade-like segment of a flower; the petals often spread outward to attract pollinating insects and/or provide a landing platform for them.
Petiole – The stem of a leaf; it connects the blade of a leaf with the stem.
Pinnate – There is a central vein along the length of the leaf, from which side veins radiate outward from an acute angle. This is the most common type of venation. See line drawing of Pinnate venation (Copyright © 1980 by Iowa State Press).
Pinnate-Pinnatifid – This expression has one of two possible meanings: 1) A compound leaf that is simple pinnate with pinnatifid leaflets throughout, or 2) A partially compound leaf that is simple pinnate with lobed or unlobed leaflets toward the base, becoming a simple leaf that is pinnatifid or bipinnatifid toward its tip. Some species of ferns have pinnate-pinnatifid leaves, e.g. Cystopteris protrusa (Fragile Fern).
Pinnate Leaf – See 'Oddly Pinnate Leaf' or 'Evenly Pinnate Leaf.'
Pinnately Lobed – The leaf has pairs of lobes arranged oppositely from each other along its length. Another name for this shape is 'pinnatifid.' See line drawing of Pinnately Lobed shape. Sometimes the lobes are not strictly opposite from each other, but appear alternately or irregularly along the side margins of the leaf.
Pinnatifid – A simple leaf that is pinnately lobed. These lobes appear on the side margins of the leaf blade. A pinnatifid leaf is not a compound leaf because it lacks true leaflets.
Pistil – The female organ of a flower consisting of a stigma, style, and the ovulum (ovary). The latter is the swollen base of the pistil that contains the ovules (immature seeds). The pistil is usually located at the center of a flower. Some flowers have compound pistils that are called "carpels."
Pistillate Flowers – Female flowers that have pistils, but no stamens; these flowers produce seeds, but no pollen.
Pistillate Scale – In Carex spp. (Sedges), each pistillate flower has a pistillate scale underneath it to provide structural support. Depending on the species, the pistillate scale can assume different sizes, shapes, or colors, although it is mostly flat and membranous. Here is a line drawing of a Pistillate Scale (Copyright © 2006 by Diana Smailus).
Plano-Convex – A surface that is flat on one side and convex on the other. This expression can refer to the shape of some leaves (flat on the upper side, convex below), or it can refer to the shape of the perigynium of some Carex spp. (flat on the interior side, convex on the exterior).
Plumose – This means 'feathery.' For example, wind-pollinated female flowers often have plumose stigmata so that they are more likely to receive the pollen of male flowers. Sometimes the hairs at the apex of a wind-dispersed achene (or seed) are called 'plumose' because they are branched and feathery in appearance, rather than straight and bristly.
Pubescent – The surface of a leaf or stem that is densely covered with fine short hairs.
Raceme – An elongated cluster of flowers arranged individually along a central stem; each flower has its own pedicel (flower stem). See line drawing of Raceme (Copyright © 1980 by Iowa State Press).
Rachilla – This is a side stalk that diverges from the central stalk (rachis) in either a compound leaf (as in ferns) or an inflorescence (as in grasses and sedges).
Rachis – This is the central stalk of either a compound leaf (as in ferns) or an inflorescence (as in grasses and sedges).
Rank Odor – Foliage that exudes a bitter aroma; this is often the result of toxic alkaloids.
Recurved – A floral structure that curls gradually outward or downward toward its tip. This often refers to the shape of floral scales for some forbs and sedges, or it can refer to the shape of leaf blades.
Reflexed – A floral structure that bends outward or downward at a sharp angle. For example, the sepals of some Trillium spp. (Trilliums) bend sharply away (usually downward) from the flower or fruit. Such sepals are 'reflexed.'
Reniform – A structure that is kidney-shaped; this often refers to the shape of seeds, particularly in the Fabaceae (Bean family). Sometimes "reniform" refers to the shape of a leaf that is broader than it is long, and slightly notched at the base of the blade.
Reticulate – The veins of a leaf form an interconnected network that is often angular and irregular; this is more typical of the lower side of a leaf, rather than the upper side. Reticulate veins are usually rather fine. See line drawing of Reticulate venation (Copyright © 1980 by Iowa State Press).
Revolute – When the margin of a leaf rolls downward. A plant species with this characteristic is Thalictrum revolutum (Waxy Meadow Rue), which has revolute leaf margins.
Rhizomatous – A rhizomatous root system has shallow underground runners (rhizomes) that can produce new plantlets some distance away from the mother plant. See line drawing of a Rhizomatous root system (Copyright © 1980 by Iowa State Press).
Rhomboid – This refers to a 3-dimensional shape that resembles a diamond or a pair of pyramids that are joined together at the base. While it is unusual, some achenes have a rhomboid shape.
Rosette – Basal leaves are arranged in a whorl close to the ground in the form of a rosette. This rosette can consist of numerous overlapping leaves. A flowering stalk may appear from the center of the rosette, with or without leaves. See line drawing of Rosette (Copyright © 1980 by Iowa State Press).
Rugose – The rough-wrinkly surface of a seed.
Rushes – This refers to species in the Juncaceae (Rush family), particularly Juncus spp. (Rushes). Rushes are distinct from plants in the Grass family (Poaceae) and Sedge family (Cyperaceae).
Sagittate – The leaf is shaped like an arrowhead. The apex of the leaf converges to a rather blunt point, while the broad base angles upward sharply toward the outer end of the petiole (leaf stem). See line drawing of Sagittate shape (Copyright © 1980 by Iowa State Press).
Scabrous – This refers to a leaf margin with a rough texture. This rough texture is the result of minute teeth along the leaf margin that are hard to see without magnification. Sometimes a scabrous leaf margin can cause lacerations on human flesh.
Scales – Among grasses (Poaceae), scales form the outer surface of the flowers in a spikelet; they are usually keeled and somewhat flattened. The lowest pair of scales in a spikelet are called the 'glumes,' while the remaining pairs of scales are called 'lemmas.' Among sedges (Cyperaceae), scales are small bractlets underneath the flowers in a spikelet. There is one scale per flower. The scales of female flowers are called 'pistillate scales,' while the scales of staminate flowers are called 'staminate scales.' Scales are often lanceolate or ovate in shape and they may have awns at their tips.
Sedges – Members of the Cyperaceae (Sedge family) are collectively known as 'sedges,' although some groups of plants in this family have other common names. The term 'sedge' is used to describe Carex spp. in particular.
Seed Capsule – This consists of the exterior wall and inner cells (if any) of the ovulum (the base of a pistil) after they have become dried out. The seed capsule contains one or more mature or nearly mature seeds. The seed capsule is often ovoid in shape and more or less open at the top, although there are many variations in form.
Seedpod – This is a more or less spongy fruit that contains one or more seeds, often in rows; it often splits apart along one or two sides to release the seeds. Seedpods have variable shapes; in the Brassicaceae (Mustard family), they are often long and cylindrical, while in the Fabaceae (Bean family), they are often flattened and oblong.
Sepal – This is often a leaf-like segment at the base of the flower; the sepals often surround the ovaries (developing seeds) and provide some structural support and protection. Sometimes the sepals have a petal-like appearance that helps to attract pollinating insects.
Septate – This describes leaf blades with cross-sectional venation that span adjacent parallel veins. Some Scirpus spp. (Bulrushes) have septate leaves with cross-sectional venation.
Serrate – The leaf margin is divided into sharp teeth of approximately the same size, like a saw. "Finely serrate" refers to small teeth, while "coarsely serrate" refers to large teeth. See line drawing of Serrate Margin (Copyright © 1980 by Iowa State Press).
Sessile – A leaf that joins the stem without a petiole, or a flower that joins the stalk without a pedicel.
Sheath – Grasses, sedges, and some forbs have an extension of the leaf that wraps around the stem (or culm). This portion of the leaf is the sheath. In contrast, the blade of a leaf is the extension of the leaf that spreads away from the stem (or culm). An 'open sheath' has a margin along the length of the culm that can be pried open and unfolded. In contrast, a 'closed sheath' completely wraps around the culm and lacks any margin. This distinction is sometimes useful in identifying a sedge or grass species.
Sheath (horsetails) – For Equisetum spp. (Horsetails), a sheath is a ring-like structure that binds neighboring joints together on a central stem. The sheaths of Horsetails often have small teeth along their upper rims.
Shoot (fertile) – A vegetative growth with flowers or spores; usually a stem with leaves is present. Fertile shoots enable a plant to reproduce sexually through flowers, or asexually through spores. Fertile shoots can also reproduce asexually through rhizomes or offsets.
Shoot (infertile) – A vegetative growth that lacks flowers or spores; it typically consists of a stem with leaves only. Infertile shoots transform solar energy into carbohydrates, which are stored in the root system. This facilitates asexual reproduction via rhizomes or offsets; it also enables a plant to survive winter dormancy and produce new shoots the following spring.
Simple Leaf – The leaves of most plants are simple; they are not divided into leaflets. See line drawing of a Simple Leaf (Copyright © 1980 by Iowa State Press).
Sinus – This refers to the indentation or bottom of a margin between two adjacent lobes of a leaf blade. Whether lateral veins terminate near the tips of leaf lobes or at their sinuses is occasionally useful in the identification of a fern.
Smooth – The leaf margin is simply and smoothly curved; this type of margin is also called "entire." See line drawing of Smooth margin (Copyright © 1980 by Iowa State Press).
Sorus – This is a spore-bearing structure of a fertile fern leaf; the plural form of this term is 'sori.' The sori are usually located on the leaf underside near the margins. The typical sorus is small, round, dark-colored, and flat to convex on its upper surface. Each sorus has many sporangia, which are even smaller spore-bearing structures.
Spadix – A spadix is a fleshy spike that bears both male and female flowers; it is often surrounded by a modified bract called a "spathe." An inflorescence with a spadix is typical of members in the Araceae (Arum family).
Spathe – A spathe is a modified bract that subtends or surrounds the flowers of some plant species. Among members of the Araceae (Arum family), this spathe surrounds the spadix; the spathe may assume colors other than green and have a petal-like appearance, although this is not always the case. Among members of the Commelinaceae (Dayflower family), there are two spathes subtending each flower; these spathes have a leafy appearance and they are more or less fused together.
Spheroid – A seed or seed capsule that is shaped like a sphere or ball.
Spike – An unbranched stalk of flowers; each flower or flowerhead is attached directly to the central stalk. See line drawing of a Spike (Copyright © 1980 by Iowa State Press). For grasses (members of the Poaceae), a spike is an unbranched stalk of spikelets; each spikelet attaches directly to the central stalk. Here is an example of a Grass Spike (Copyright © 2006 by Diana Smailus).
Spike Rushes – This expression refers to species in the genus Eleocharis. Because Eleocharis spp. are members of the Cyperaceae (Sedge family), they are actually sedges, not rushes.
Spikelet – This typically refers to a floral structure in the grass and sedge families that consists of pairs of floral scales that are stacked on top of each other. Aside from the bottom pair, each pair of scales in a spikelet contains a single floret. For grasses, the bottom pair of scales in a spikelet are referred to as 'glumes,' while the remaining scales are called 'lemmas.' Sometimes the lemmas occur individually, rather than in pairs. The structure of a spikelet is typically columnar and flattened. A spikelet can have from one to many florets; this varies with the species. In the inflorescence of a grass or sedge, the spikelets are organized into a panicle, raceme, or spike, as described elsewhere. Here is a typical example of a Spikelet (Copyright © 2006 by Diana Smailus).
Sporangium – This is an individual spore-bearing structure within the sorus of a fern. Each sorus has many sporangia (plural form of sporangium). A typical sporangium is club-shaped, consisting of a stalk with a small ovoid or globoid structure at its apex. This latter structure pops open to release the individual spores of a fern.
Spores – Spores are produced by ferns, horsetails, and other primitive plants. Spores resemble tiny seeds, but they lack food for the plant embryo. Because spores are easily carried aloft by the wind, they allow ferns and horsetails to reproduce asexually across considerable distances. However, some species of plants, e.g. Isoetes spp. (Quillworts), reproduce sexually by producing both male and female spores. Because the female spores are larger in size than the male spores, they are referred to as 'macrospores.'
Spur – The spike-like posterior of a corolla that contains nectar; this spur can be straight or curved, long or short. The flowers of Delphinium spp. (Delphiniums) and Linaria spp. (Toadflaxes) have such spurs.
Stamens – The male reproductive organs of a flower; a stamen consists of a thread-like filament with a pollen-bearing anther at its apex.
Staminate Flowers – Male flowers that have stamens, but no pistils; these flowers produce pollen, but no seeds.
Stigma – The tip of a pistil that receives the pollen. The stigma is often knobby or swollen; sometimes it is divided into 2 or 3 short segments, in which case the stigma is bipartite or tripartite.
Stipe – This is a pointed slender appendage that defines the inner tip of a seedpod; the seedpods of many plant species lack stipes.
Stipules – A leaf-like structure that occurs where the leaf joins the stem; stipules occur in pairs.
Stoloniferous – A stoloniferous root system has above ground runners (stolons) that can produce new plantlets some distance away from the mother plant. See line drawing of a Stoloniferous plant (Copyright © 1980 by Iowa State Press). Stolons are actually modified stems, rather than roots, but their function is similar to rhizomes.
Style – This is a long and thread-like structure that connects the stigma with the ovary. A flower may have a single style, or several of them.
Subleaflet – Some compound leaves have compound leaflets that are subdivided into simple subleaflets. An example of a plant with such subleaflets is Osmunda regalis (Royal Fern).
Taproot – The root system consists of a central taproot that originates from the base of the plant. This taproot can be slender or rather stout, and usually has fine rootlets towards the growing point. See line drawing of a Taproot (Copyright © 1980 by Iowa State Press).
Tepals – Refers to the petals and sepals of many species in the Liliaceae (Lily family), which typically have 3 petals and 3 petal-like sepals with a similar appearance.
Terete – A stem with a circular cross-section; sometimes this stem has fine ridges that produce a cross-section that resembles a multisided polygon.
Trifoliate Leaf – A compound leaf with 3 leaflets originating from the same location at the end the petiole (leaf stem). This is a special case of a palmate compound leaf. See line drawing of a Trifoliate Leaf (Copyright © 1980 by Iowa State Press).
Truncate – This often refers to the shape of ray florets or achenes among members of the Asteraceae (Aster family). A ray floret with a flattened outer tip is "truncate." Similarly, an achene with a flattened upper end is "truncate."
Tubercle – This is a small bump or wart-like structure on the surface of a floral structure. This typically refers to the surface of an achene (seed), which may have a single tubercle, or its surface may be more or less covered with a multitude of minute tubercles. Sometimes 'tubercle' refers to the spore-bearing structures on horsetails and ferns, which often have a bumpy appearance.
Tuberculate – The granular-pebbly surface of a seed.
Tuberous – A tuberous root system consists of a loose collection of coarse roots that occasionally thicken into fleshy underground tubers. These tubers store water and energy for the plant. Occasionally, rhizomes develop from the tubers that can produce new plantlets. See line drawing of Tuberous root system (Copyright © 1980 by Iowa State Press).
Tussock – The dense mat of roots at the base of some plants push the ground upward to form a mound, which is called a 'tussock.' Such plants often have multiple stems that develop directly from the tussock; this includes some species of grass, sedge, and fern.
Umbel – A cluster of flowers in which the pedicels (flower stems) originate from the same central location. See line drawing of Umbel (Copyright © 1980 by Iowa State Press).
Umbellets – The smaller secondary umbels of a compound umbel of flowers.
Undulate – The leaf margin gently undulates like a wave; the undulation is often irregular. See line drawing of Undulate margin (Copyright © 1980 by Iowa State Press).
Valve – Some seed capsules are divided into cells with rounded exterior walls. The protruding walls of these cells are often referred to as "valves." Thus, a 3-celled seed capsule with 3 protruding walls is "3-valved." This also refers to the shape of the ovulum (base of the pistil) when such cells are present.
Whorled – The leaves are arranged in whorls of 3 or more leaves along the stems of a plant. The petioles or bases of a whorl of leaves meet together at the same location of the stem, while their tips point outward in different directions, like the spokes of a wheel. See line drawing of Whorled leaves (Copyright © 1980 by Iowa State Press).
Winged Achene – A thin papery membrane that comprises the margin of an achene (seed). As a result, the achene is more readily dispersed by the wind.
Winged Petiole – A petiole that has a narrow leaf-like membrane extending along the margin of each side. These leafy margins are the "wings" of the petiole.