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(Last Modified On 1/28/2013)
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(Last Modified On 1/28/2013)
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Genus
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ALTERNANTHERA Forskal
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PlaceOfPublication
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Fl. Aeg.-Arab. 28. 1775.
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Description
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Flowers perfect, bracteate and bibracteolate, sessile or subsessile in spikes or glomes. Sepals 5, discrete, hypogynous, concave, subequal or strongly dissimilar, white to purple, the bases often indurate. Stamens 3-5, the filaments flattened and united below into an entire or appendiculate tube; anthers 2-locellate, oblong, introrse, medially attached. Ovary globose to obovoid, often compressed, 1 -locular, 1-ovulate; ovule carn-pylotropous on an elongate funicle; stigma 1, capitate or obscurely bilabiate, on a short or elongate style. Fruit a membranaceous utricle, indehiscent; seeds cochleate-orbicular, smooth. Glabrous to copiously pubescent erect, scandent or prostrate annuals or perennials. Leaves opposite, sessile or petiolate, entire to denticulate, glabrous to densely pubescent, mostly herbaceous. Inflorescences of axillary and terminal sessile or pedunculate spikes or glomes. This genus of over 100 species is best developed in the Americas, although many species are ubiquitous weeds. Some species are cultivated for their ornamental inflorescences and others are planted as tufted border plants and soil binders.
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Note
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Alternanthera axillaris Hornem. and A. repens (L.) Gmel. are rather obnoxious weeds with pungent sepals. Working under the American Code of nomenclature, Standley (in Jour. Wash. Acad. 5:72. 1915) explains the rather complicated reasons which led him to transfer the Alternanthera species to Achyranthes, a treatment which he later abandoned. Hitchcock & Green (in Brittonia 6:114. 1947) have proposed that Alternanthera repens (L.) Gmel. be the lectotype of the genus. Eleven species are reported from Panama.
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Key
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a. Inflorescences sessile in the axils of small leaves (mostly 1-4 cm. long); outer and inner sepals strongly dissimilar, the outer 1.5-2 times as broad as the inner (sepals subequal but exceeded by the utricle in A. sessilis) prostrate or decumbent herbs. b. Utricle longer than the sepals; sepals subequal acute, 1-nerved, glabrous; pubescence of simple hairs. -- - 1. A. SESSILIS bb. Utricle shorter than the sepals; sepals dimorphic or trimorphic, accuminate to aristate, 3-5 nerved, pubescent; pubescence of stellate or septate hairs. c. Filaments longer than the pseudostaminodia; stigmata as long as or longer than the styles, attaining or exceeding the anthers; sepals dimorphic or trimorphic; prostrate plants with the leaves often less than 1.5 cm. long. d. Inflorescences subglobose to cylindric; sepals dimorphic, the outer 3 subequal with flexible awns if any, whitish; bracteoles 0.2-0.5 as long as the sepals; stigmata longer than the styles; seeds 1-1.2 mm. broad .----------- ---- 2. A. POLYGONOIDES dd. Inflorescences mostly cylindric; sepals trimorphic, with 2 of the outer 3 aristate with rigid awns, stramineous, the third sepal 0.5-1 mm. shorter, merely acuminate; bracteoles more than half as long as the sepals; stigmata about as long as the styles; seeds 1-1.5 mm. broad ............ . 3. A. REPENS cc. Filaments shorter than the pseudostaminodia; stigmata shorter than the styles, exceeded by the anthers; sepals dimorphic; prostrate or decumbent herbs, the leaves often over 1.5 cm. long. e. Leaves apically acute or acuminate, glabrate or sparsely strigose below .-----------------------------4. A. FICOIDEA ee. Leaves apically rounded, densely cinereous-pubescent below with stellate hairs ............................................... 5. A. HALIMIFOLIA aa. At least some of the inflorescences pedunculate in the axils of larger leaves (mostly 4-10 cm. long); outer and inner sepals subequal; erect or clambering shrubs or decumbent aquatics. f. Sepals 5-6 mm. long, 3-4 times as long as the bracts; glomes white, 10-18 mm. broad; peduncles unbranched, mostly less than 5 cm. long; subglabrous herbaceous aquatic plants ............ 6. A. PHILOXEROIDES ff. Sepals 2-6 mm. long, no more than twice as long as the bracts; inflorescences white to purple, 4-12 mm. broad; peduncles branched or unbranched, 1-9 cm. long; glabrate to densely pubescent suffruti- cose terrestrial plants. g. Glomes 9-12 mm. broad, if narrower, subsessile; sepals 4-6 mm. long. h. Peduncles mostly simple and exceeded by the subtending leaves; leaves ovate, short-strigose or glabrate; sepals short-strigose, the hairs mostly less than 2 mm. long; styles 1-2 times as long as the stigmata; pseudostaminodia almost as long as the sepals. - 7. A. WILLIAMSII hh. Peduncles mostly trichotomously branched and exceeding the subtending leaves; leaves lanceolate, sericeous below; sepals pubescent with long beaded hairs, many of the hairs 3-5 mm.. long; styles 2-3 times as long as the stigmata; psetudostaminodia about half as long as the sepals-..,.,, ... ..................... 8. A. LAGUROIDES gg. Spikes 4-7 mm. broad, pedunculate; sepals 2-3.5 mm. long. i. Leaves linear to linear-elliptic, 2.5-5 cm. long, 3-6 mm. broad; peduncles unbranched; flowers stramineous .........,,,,...... 9. A. STENOPHYLLA ii. Leaves ovate to elliptic, 2.5-10 cm. long, 6-50 mm. broad; peduncle branched or unbranched; flowers white, stramineous or purple. j. Peduncles unbranched; flowers white to stramineous; seeds - reddish brown; styles about twice as long as the stigmata-...... 10. A. MEXICANA jj. Peduncles branched; flowers purplish; seeds reddish brown to black; styles about as long as the stigmata. ........ 1. A. PANAMENSTS
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