31. Amaranthus polygonoides Linnaeus, Pl. Jamaic. Pug. 27. 1759.
Smartweed amaranth, tropical amaranth
Amaranthus berlandieri (Moquin-Tandon) Uline & W. L. Bray
Plants annual, glabrescent proximally, pubescent distally, becoming glabrous at maturity. Stems erect-ascending to pro-strate, branched mostly at base and in proximal 1/2, 0.1-0.5 m. Leaves: petiole ± equaling blade; blade ovate, obovate-rhombic to narrowly ovate, sometimes lanceolate, 1.5-3(-4) × 0.5-1.5(-2) cm, base cuneate, margins entire to undulate-erose, apex rounded, obtuse, or emarginate, mucronate. Inflorescences axillary, congested clusters. Bracts of pistillate flowers lanceolate or linear, 1-1.5 mm, 1/2 as long as tepals. Pistillate flowers: tepals 5, connate in proximal 1/3 (entirely distinct in all other species), with 3 prominent veins abaxially, spatulate or somewhat clawed, equal or subequal, 2-3 mm, apex rounded or retuse, mucronate; style branches somewhat spreading; stigmas 3. Staminate flowers intermixed with pistillate; tepals (4-)5; stamens 2-3. Utricles cylindric or narrowly turbinate, 2-2.5 mm, ± equaling tepals, smooth proximally or roughened toward tips, indehiscent or tardily dehiscent. Seeds dark reddish brown to black, lenticular, 0.8-1 mm diam., shiny.
Flowering summer-fall. Disturbed habitats, coastal areas, near wool-combing mills; 0-500 m; Fla., S.C., Tex.; Mexico; West Indies; n South America; rarely introduced in Europe and some other regions.
Amaranthus berlandieri often has been recognized as a separate species related to A. polygonoides. J. Henrickson (1999) clarified the confusion that existed in earlier descriptions of these two taxa and showed that the main characters used for their separation (dehiscent versus indehiscent utricles, leaf shape, etc.) are inconsistent and cannot be applied for segregation of two independent species. The subspecies rank may be more appropriate for A. berlandieri, as was suggested by A. Thellung (1914-1919). The relationships between these taxa of the A. polygoniodes aggregate require additional study; in the present treatment we follow the solution proposed by Henrickson.
