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Weed Index A B C D E F G H I J K L M N O P Q R S T U V W X Y Z PPWS Department Weed Control Guide Extension Publications Aquatic Weeds Weed Key for Grasses Weed I.D. References Scientific Name Index Weed Identification Guide These pages are intended to aide in the identification of common weeds and weed seedlings found throughout Virginia and the Southeastern U.S. The weed pictures in this guide are arranged alphabetically by common name and may be viewed by clicking on one of the letters to the left. Please take some time to view a list of references used in the assembly of the botanical descriptions for weeds contained within this guide. Descriptions for all weeds are not complete at this point. However, additions are being made daily. Only pictures of the highest quality have been included in this guide, therefore each page may take some time to download. Try our GRASS WEED IDENTIFICATION KEY. By answering a series of questions about your unknown grass sample, this identification key will narrow down your choices and provide you with the identity of your unknown grass sample . View and download our extension publications on the identification and control of perennial weeds in Virginia. Try our new scientific name index. This new option allows you to search all of the weeds in this guide alphabetically according to scientific name. Feel free to e-mail any comments or suggestions to: Kevin Bradley Web Page Author Scott Hagood Extension Weed Scientist http://www.ppws.vt.edu/weedindex.htm (1 of 2) [5/12/2004 6:31:37 PM] http://www.ppws.vt.edu/weedindex.htm (2 of 2) [5/12/2004 6:31:37 PM] Common Weed Names: A Common Name Scientific Name Alligatorweed Alternanthera philoxeroides Amaranth, Palmer Amaranthus palmeri Amaranth, Prostrate Amaranthus blitoides Amaranth, Spiny Amaranthus spinosus American Burnweed Erechtites hieracifolia American Elderberry Sambucus canadensis American Speedwell Veronica americana American Water Plantain Alisma subcordatum American Water Willow Justicia americana Annual Bluegrass Poa annua Annual Fleabane Erigeron annuus Annual Jewgrass Microstegium vimineum Annual Ryegrass Lolium multiflorum Annual Sowthistle Sonchus oleraceus Apple-of-Peru Nicandra physalodes Arrowhead, Long-beaked Sagittaria australis Arrowleaf Sida Sida rhombifolia Arrow-leaved Tearthumb Polygonum sagittatum Arthraxon, Jointhead Arthraxon hispidus Artichoke, Jerusalem Helianthus tuberosus Asian Dayflower Murdannia keisak Common Weed Names: A http://www.ppws.vt.edu/scott/weed_id/indexa.htm (1 of 2) [5/12/2004 6:31:38 PM] Asian Spiderwort Murdannia keisak Asiatic Dayflower Commelina communis Aster, White Heath Aster pilosus Autumn Olive Elaeagnus umbellata Common Weed Names: A http://www.ppws.vt.edu/scott/weed_id/indexa.htm (2 of 2) [5/12/2004 6:31:38 PM] Virginia Tech Weed Identification Guide Alligatorweed: Alternanthera philoxeroides Weed Description: Aquatic mat-forming perennial that usually spreads vegetatively by fragmentation. Alligatorweed is an invasive aquatic weed that can be found in the coastal plain from Virginia to Florida and westward to Texas. This weed is now also found in coastal California. Leaves: Opposite, elliptic in outline, from 2 to 4 inches in length. Leaves have a distinctive midrib, are without hairs (glaucous), and are without petioles. Stems: Fleshy and succulent, light to dark green or pink to purplish in color, and reach 3 feet in length. Stems root at the nodes and are usually floating or trailing along the ground except for the tips that turn upward (decumbent). Stems are generally without hairs (glabrous) except for a few that occur at the leaf base. Roots: Fibrous roots occur at the stem nodes. Roots can be free-floating in water or occur in the soil. Flowers: Relatively small (13 mm in diameter) and white in color. Flowers occur on flower stalks (peduncle) that are approximately 1/2 to 3 inches in length. Flowering usually occurs from April through October. Identifying Characteristics: Aquatic mat forming perennial with hollow stems, opposite leaves, and solitary white flowers. Alligatorweed http://www.ppws.vt.edu/scott/weed_id/alrph.htm [5/12/2004 6:31:41 PM] Select a Resource... Virginia Tech Weed Identification Guide Palmer Amaranth: Amaranthus palmeri Weed Description: An erect summer annual that may reach 6 1/2 feet in height. Palmer amaranth closely resembles many other pigweed species, and is found throughout the southern United States from southern California to Virginia. Seedling: Stems below the cotyledons (hypocotyls) are without hairs (glabrous) but may sometimes be slightly hairy, and are often red in color. Cotyledons are narrow (10-12 mm long) and green to reddish in color on the upper Palmer Amaranth http://www.ppws.vt.edu/scott/weed_id/amapa.htm (1 of 5) [5/12/2004 6:31:50 PM] Select a Resource... surface. Lower surfaces of cotyledons have a reddish tint. First true leaves are alternate, ovate in shape, and are slightly notched at the tip of the leaf blade (apex). Leaves: Alternate, without hairs (glabrous), and lance-shaped or egg-shaped in outline. Leaves are 2 to 8 inches long and 1/2 to 2 1/2 inches wide with prominent white veins on the undersurface. Leaves occur on relatively long petioles. Roots: Taproot that is often, but not always, reddish in color. Fruit: A single seeded utricle that reaches 2 mm in length and are wrinkled when Palmer Amaranth http://www.ppws.vt.edu/scott/weed_id/amapa.htm (2 of 5) [5/12/2004 6:31:50 PM] dry. Each utricle splits open in the middle to expose a single glossy black to dark brown seed that is 1 to 1.2 mm long. Stems: One central stem occurs from which several lateral branches arise. Palmer Amaranth http://www.ppws.vt.edu/scott/weed_id/amapa.htm (3 of 5) [5/12/2004 6:31:50 PM] Flowers: Small, green, inconspicuous flowers are produced in dense, compact, terminal panicles that are from 1/2 to 1 1/2 feet in length. Smaller lateral inflorescences also occur between the stem and the leaf petioles (leaf axils). Male and female flowers occur on separate plants. Each terminal panicle contains many densely packed branched spikes that have bracts that are 3 to 6 mm long. Identifying Characteristics: Dense, compact terminal panicles and relatively tall plants with alternately arranged leaves with petioles that are longer than the leaves. Palmer amaranth is often confused with other similar pigweed species. However, no other pigweed species have terminal panicles that reach 1 1/2 feet in length. Additionally, the terminal spike of palmer amaranth is much smoother and narrower and less spike-like than either Redroot Pigweed (Amaranthus retroflexus) or smooth pigweed (Amaranthus hybridus). The leaves of palmer amaranth are Palmer Amaranth http://www.ppws.vt.edu/scott/weed_id/amapa.htm (4 of 5) [5/12/2004 6:31:50 PM] also without hairs and have prominent white veins on the undersurface unlike those of redroot pigweed. These species may also resemble Common Lambsquarters (Chenopodium album) in the cotyledon stage, however common lambsquarter's cotyledons often have a mealy gray cast and the first true leaves are alternate, unlike any of the pigweed species. Palmer Amaranth http://www.ppws.vt.edu/scott/weed_id/amapa.htm (5 of 5) [5/12/2004 6:31:50 PM] Virginia Tech Weed Identification Guide Redroot Pigweed: Amaranthus retroflexus Weed Description: An erect summer annual that may reach 6 1/2 feet in height. Redroot pigweed is an abundant seed producer that may be found throughout the United States in horticultural, nursery, and agronomic crops, landscapes, roadsides, and also in pastures and forages. Seedling: Stems below the cotyledons (hypocotyls) are without hairs (glabrous) but may sometimes be slightly hairy, and are often red in color, especially near the base. Cotyledons are narrow (10-12 mm long) and Redroot Pigweed http://www.ppws.vt.edu/scott/weed_id/amare.htm (1 of 4) [5/12/2004 6:31:54 PM] Select a Resource... green to reddish in color on the upper surface. Lower surfaces of cotyledons have a reddish tint. First true leaves are alternate, ovate in shape, and are slightly notched at the tip of the leaf blade (apex). Hairs may occur on the leaf margins and along veins, especially along the lower leaf surfaces. Leaves: Alternate, ovate in outline, with petioles that reach 1/2 inch in length. Leaves have wavy margins and hairs that occur along the veins of the lower leaf surfaces. Redroot Pigweed http://www.ppws.vt.edu/scott/weed_id/amare.htm (2 of 4) [5/12/2004 6:31:54 PM] Stems: Stout, erect, branched, and reaching 6 1/2 feet in height. Stems usually have short hairs, especially near the upper portions of the plant. Roots: A shallow taproot that is often, but not always, reddish in color. Fruit: A single seeded utricle that reach 2 mm in length and are wrinkled when dry. Each utricle splits open in the middle to expose a single glossy black to dark brown seed that is 1 to 1.2 mm long and ovate in outline. Flowers: Small, green, inconspicuous flowers are produced in dense, compact, terminal panicles that are approximately 3/4 inch wide and from 2 to 8 inches in length. Smaller inflorescences also occur between the stem and the leaf petioles (leaf axils). Male and female flowers occur on the same plant (monoecious). Each terminal panicle contains many densely packed branched spikes that have bracts that are 4 to 8 mm long and 2-3 times longer than the sepals. Redroot Pigweed http://www.ppws.vt.edu/scott/weed_id/amare.htm (3 of 4) [5/12/2004 6:31:54 PM] Identifying Characteristics: Dense, compact terminal panicles and relatively tall plants with alternately arranged leaves. Redroot pigweed is often confused with other similar pigweed species. For example, smooth pigweed is very similar, however this species has terminal panicles that appear less dense, compact, and bristly than those of redroot pigweed. Additionally, the bracts of smooth pigweed are only slightly longer than the sepals, unlike those of redroot pigweed. Palmer Amaranth (Amaranthus palmeri) also resembles redroot and smooth pigweed, however the terminal panicles of this species are much longer and narrower than the other pigweed species. These species may also resemble Common Lambsquarters (Chenopodium album) in the cotyledon stage, however common lambsquarter's cotyledons often have a mealy gray cast, and the first true leaves are alternate, unlike any of the pigweed species. Redroot Pigweed http://www.ppws.vt.edu/scott/weed_id/amare.htm (4 of 4) [5/12/2004 6:31:54 PM] Virginia Tech Weed Identification Guide Common Lambsquarters: Chenopodium album Weed Description: Summer annual to 3 1/2 feet in height capable of producing thousands of seeds. Seedling: Cotyledons elliptic (12-15 mm long), dull green with a mealy gray cast on the upper surface and maroon on the underside, turning green with age. Hypocotyls are hairless, green or tinged with maroon. The first pair of true leaves are opposite, all other leaves are alternate. Seedling leaves are triangular and also have a mealy gray cast. Leaves: Alternate, light green, rounded, triangular, 1 1/4 to 10 inches long and on a long petiole. Common Lambsquarters http://www.ppws.vt.edu/scott/weed_id/cheal.htm (1 of 3) [5/12/2004 6:31:58 PM] Select a Resource...