Introduction to Weed Identification

Identifying plants is essential to get access to what other people have learned. Here are some of the features of plants that distinguish one from another and a glossary of the common terms used to label the features. Since some distinguishing features of plant flowers are quite small, you will need a hand lens of 10x magnification or a smart phone magnifier. My phone’s camera provides 8x magnification, but that’s not quite enough. The glossary follows the illustrations.

Weed Anatomy Images

Grass spikelet. Artist unknown (link broken).

Weed Anatomy Glossary

• Achene – Small dry one-seeded fruit in which the ovary wall is free from the seed
• Acuminate – Gradually tapering to a sharp point
• Acute – Sharp pointed but less tapering than acuminate; angle less than 90 degrees
• Allelopathic – Produces biochemicals that prevent the germination, growth, survival, or reproduction of neighboring plants
• Annual – Plant that usually germinates, flowers, and dies in one growing season
• Anther – Enlarged part at the top of the stamen; bears the pollen
• Attenuate – Gradually narrowing to a slender apex or base
• Auricle – Some grasses have small claw-like extensions of the collar that separates the sheath from the blade
• Awn – More or less stiff bristle on the end of lemmas or glumes
• Axil – Upper surface of angle between the stem and the leaf
• Blade – Grass leaf above the sheath
• Bract – Modified leaf underneath a flower or inflorescence
• Bristle – Stiff, slender appendage
• Bunchgrass – Grass without stolons or rhizomes; growth forms a bunch
• Bur – Rough or prickly envelope around a seed or fruit
• Calyx – Outer set of floral leaves, usually green, composed of all the sepals
• Caryopsis – Dry one-seeded fruit in which the ovary wall unites with the seed coat, typical of grasses
• Ciliate – Fringed with hairs on edge
• Collar – Region of the outer side of the grass leaf at the junction of the blade and sheath
• Compound – Leaves divided into leaflets
• Convolute – Rolled longitudinally
• Corolla – All the flower petals
• Creeping – Spreading just under the surface of the soil
• Culm – Stem of grass plants
• Cyathia – Euphorbia flowers appear to be individual flowers, but they are composed of bracts fused into a cup (involucre), with peripheral nectary glands supported by petal-like (petaloid) bracts. Within the cup, there is a ring of male flowers, each with a single stamen. Out of the middle protrudes a single, stalked female flower with no petals
• Deciduous – Sheds leaves at the end of the growing season. Induced by cold temperature or by drought
• Decumbent – Stems that lie flat and turn up at their ends
• Decurrent – Extending downward from the point of attachment
• Dehiscent – Splitting open at maturity
• Dioecious – Plants with only male (staminate) flowers
• Disk flowers – Tubular flowers in the center of the flower heads in the aster/sunflower family
• Distally – Opposite point of attachment
• Embryo – Young plant enclosed in a seed
• Entire – Continuous margin
• Entity – Natural vegetation unit defined by particular plant species
• Erose – Irregularly notched at the apex; appearing gnawed or eroded
• Flexuous – Bent alternately in opposite directions; a wavy form
• Floret – Small flower in the spikelet of the grasses, or the flower head of the sunflower family
• Floret – Individual grass flower including its two bracts, lemma and palea, or flower heads in the sunflower family
• Flower head – Dense inflorescence of sessile (stalkless) flowers
• Fruit – Seed case or seed pod (the ripened ovary); containing one to many seeds
• Geniculate – Bent sharply, like a knee
• Glabrous – Smooth without hairs
• Glands – Secreting tissue
• Glaucous – Powdery or waxy surface cover
• Glumes – Two thin bracts surrounding the spikelet of a grass (forming the husk of a cereal grain); or one surrounding the florets of a sedge
• Grain – The seed-like dispersal unit of the grass family
• Hirsute – With straight rather stiff hairs
• Hispid – With long stiff hairs
• Hyaline – Colorless and translucent
• Imperfect – Flowers with either pistils or stamens; unisexual
• Indehiscent – Not opening at maturity
• Inferior ovary – Sepals, petals, and stamens appear to rise from the very top of the ovary
• Inflorescence – Flowering part of a plant
• Internode – Part of a stem between two successive nodes
• Introduced -Species people brought to North America
• Invader – undesirable plants that invade and replace native vegetation
• Involucre – Cluster of bracts below the inflorescence or cone (involucrate = having an involucre)
• Involute – Rolled inward on the upper (dorsal) surface
• Keel – Central dorsal ridge; the two united petals in some legume flowers
• Knotty – Hardened mass at the base or nodes
• Lacerate – Appearing torn at the edge or irregularly cleft
• Leaflet – Division of a compound leaf
• Lemma – Lower bract of the two bracts of a grass floret
• Ligule – A thin lining on the inner side of the leaf sheath at its junction with grass and sedge blades
• Ligule – the membranous, toothed, or hairy appendage on the inside of a leaf exposed at the junction of the sheath and blade
• Membranous – Thin, like a papery membrane
• Monocarpic – Flowering and bearing fruit only once and then dying; can apply to annuals, biennials, or perennials
• Monoecious – Plants with only female (carpellate) flowers
• Mycorrhiza – Formed by a combination of underground threads usually associated with plant roots
• Native – Species that originated in North America
• Nerve – Vein on glume, lemma, or palea
• Node – Place on a stem where leaves and branches originate
• Nutlet – Small nut; the one-seeded portion of a larger fruit that separates at maturity
• Obtuse – blunt or rounded (apex or base), usually making an angle of more than 90 degrees
• Ovary – Base of the female part of the flower (pistil); ripens into the fruit
• Palea – Innermost of the two bracts of a grass floret
• Panicle – Loose, irregularly branched inflorescence with stalked individual flowers
• Pappus – (plural pappi) Modified calyx of a disk or rayflower in the sunflower family; consists of awns, scales, or bristles at the apex of the achene. Facilitates wind dispersal
• Pedicel – Stalk of a spikelet
• Perennial – Plant living more than 1 year
• Perfect flowers – Both male and female reproductive parts in the same structure
• Perianth – Outer part of flowers, consisting of the calyx (sepals) and corolla (petals)
• Petaloid – Petallike
• Phyllary – In asters, a bract that with others forms the involucre or cup that holds the flowers
• Pilose – Covered with soft hair
• Pinnate – Leaf divided into leaflets along a central stem
• Pistil – Female reproductive structures of a flower
• Polycarpic – Produces flowers or spores more than once during lifetime
• Pubescent – Covered with soft hairs
• Raceme – A flower cluster with the separate flowers on short equal stalks at equal distances along a central stem (rachis). The flowers at the base of the central stem develop first
• Ray flower – Marginal petal flowers in the inflorescence of the aster/sunflower family
• Retrorse – Directed back or downward
• Rhizomatous – Having rhizomes
• Rhizome – Horizontal underground stem
• Rosette – Cluster of spreading or radiating basal leaves
• Runner – Horizontal aboveground stem; a stolon
• Scabrous – Roughened with stout projections
• Sepal – One of the outer set of floral leaves forming the calyx, usually green
• Sessile – Stalkless leaves or flowers
• Sheath – In grasses, the basal portion of the leaf forms a tube (sheath) wrapping around the stem
• Silicles – Dry, dehiscent fruit of the Brassicaceae with two parts that separate at maturity; fruit is typically less than three times as long as wide
• Silique – Dry, dehiscent fruit of the Brassicaceae with two parts that separate at maturity; fruit is typically more than three times as long as wide
• Sod-grass – Grass with stolons or rhizomes; may form continuous thatched surface
• Spatulate – Narrow at the stem widening to the tip
• Spike – An unbranched inflorescence with stalkless flowers
• Spikelet – the part of a grass inflorescence consisting of two glumes and one or more florets
• Stamen – The male portion of the flower
• Stipules – Pair of tongue-like appendages at the base of the leaf
• Stolon – Horizontal stem that roots along its length to form new plants; aboveground or at very shallow depth
• Stoloniferous – Bearing stolons
• Striate – Marked with slender, longitudinal grooves or lines, appearing striped
• Strigose – Stiff, straight hairs laying on a surface
• Succulent – Soft and fleshy in texture
• Tomentose – Covered by dense matted and tangled hairs
• Truncate – “Cut off” at the base or apex
• Truncate-ciliate – Ligule with short fringe of hair tips
• Tuber – A swollen underground stem
• Umbel – Flower stalks arising from a common point a bit like an umbrella blown inside out.
• Utricle – Small thin-walled fruit with covering more loose and fragile than that of an achene. Common among Amaranths. The Tumble Pigweed drawing and one of the photos illustrate the utricle.
• Villous- Densely hairy with long, soft hairs
• Whorl – Three or more leaves or flowers arising from the same node