Home Flora of Missouri
Home
Name Search
Families
Volumes
Amaranthus spinosus L. Search in The Plant ListSearch in IPNISearch in Australian Plant Name IndexSearch in NYBG Virtual HerbariumSearch in Muséum national d'Histoire naturelleSearch in Type Specimen Register of the U.S. National HerbariumSearch in Virtual Herbaria AustriaSearch in JSTOR Plant ScienceSearch in SEINetSearch in African Plants Database at Geneva Botanical GardenAfrican Plants, Senckenberg Photo GallerySearch in Flora do Brasil 2020Search in Reflora - Virtual HerbariumSearch in Living Collections Decrease font Increase font Restore font
 

Published In: Species Plantarum 2: 991. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 8/4/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Introduced

 

Export To PDF Export To Word

12. Amaranthus spinosus L. (spiny pigweed, thorny amaranth, careless weed)

Pl. 198 c, d; Map 821

Plants monoecious. Stems 30–150 cm long, erect or ascending, glabrous or nearly so, with conspicuous pairs of slender, straight, spreading spines at most nodes. Leaves mostly long-petiolate. Leaf blades 2–10 cm long, narrowly ovate to ovate, narrowed or tapered to a bluntly or sharply pointed tip, narrowed or tapered at the base, glabrous or nearly so. Inflorescences dull or grayish green, occasionally dull reddish-tinged; axillary and terminal; the axillary inflorescences dense, small, globose clusters or elongate spikes; the terminal inflorescence a spike or panicle with few to rarely numerous ascending branches; the flowers often grouped into discontinuous clusters or regions along the basal portions of the spikes; the tip straight or somewhat curved at maturity; the main axis and branches glabrous or nearly so. Bracts 0.5–1.0 mm long, shorter than the sepals, lanceolate to narrowly lanceolate or linear, narrowed or tapered to a sharply pointed tip, with a somewhat thickened green midrib and relatively narrow, thin, papery margins, the midrib not or only slightly extending beyond the main body as a minute, sharp point. Staminate flowers with 5 more or less similar sepals, these 1.0–1.6 mm long, somewhat outward-curved, oblong-lanceolate, narrowed or tapered to a sharp point at the tip. Stamens 5. Pistillate flowers with 5 more or less similar sepals, these 1.0–1.6 mm long, somewhat outward-curved, oblong to oblong-elliptic or oblong-lanceolate, narrowed or tapered to a blunt or sharp point. Stigmas 3, ascending to erect. Fruits 1.5–2.0 mm long, dehiscing irregularly or less commonly indehiscent or with more or less circumscissile dehiscence, the surface somewhat roughened or wrinkled above the midpoint when dry. Seeds 0.7–1.0 mm in diameter, rounded along the rim, the surface black. 2n=32, 34. June–October.

Introduced, scattered, mostly south of the Missouri River (probably originally a native of New World tropics, now distributed nearly throughout tropical and warm-temperate regions, in North America introduced north to California, Nebraska, Minnesota, and Maine; also Canada). Bottomland forests, banks of streams and rivers, and margins of sloughs; also fallow fields, crop fields, barnyards, feedlots, pastures, roadsides, railroads, and open, disturbed areas.

 


 

 
 
© 2024 Missouri Botanical Garden - 4344 Shaw Boulevard - Saint Louis, Missouri 63110