Senna roemeriana
Senna obtusifolia
Roemer senna, twoleaf senna, twoleaf wild sensitive plant
blunt leafed senna, Chinese senna, Java-bean, sickle-pod wild senna, sicklepod
1–5-flowered;
bracts caducous.
usually 1 or 2(or 3)-flowered;
bracts caducous.
9–16 mm.
7–28 mm.
monosymmetric;
calyx caducous, pale green;
corolla yellow or orange-yellow, longest petal 12–17 mm;
androecium not heterantherous, stamens 7, staminodes 3;
anthers 2.2–3.3 mm, dehiscing by 1 apical pore, apical appendage 0;
gynoecium nearly linear, ovules 22–40;
ovary densely hairy;
style slightly incurved.
asymmetric, enantiostylous;
calyx pale green;
corolla pale yellow, longest petal 9–15 mm, 1 lower petal conspicuously larger;
androecium heterantherous, stamens 7, middle stamens 1/2 as long as abaxial or smaller, staminodes 3;
anthers of middle stamens 1–2.8 mm, of abaxial stamens 2–5 mm, dehiscing by U-shaped slit, apical appendage inconspicuous, cupped;
gynoecium incurved, ovules 16–38;
ovary hairy;
style incurved.
erect, subcylindrical, straight or slightly curved, 20–35 × 4.5–6.5 mm, corrugated over seeds, dehiscing apically downward.
erect or curved downward, flat, straight, 60–180 × 2.5–6 mm, faintly corrugated over seeds, indehiscent.
brown or pinkish brown, paddle-shaped or pyriform.
dark reddish brown, rhomboid or subcylindroid-oblong.
= 28.
= 24, 26, 28.
Senna roemeriana
Senna obtusifolia
Senna obtusifolia is one of the most widespread weedy sennas native to the Americas (H. S. Irwin and R. C. Barneby 1982) and is probably naturalized circumtropically. The species is considered a noxious weed in many countries, posing problems especially for agriculture; it is able to completely invade pastures by dominating grass species, it strongly competes with crops, affecting yields negatively, and, although generally unpalatable to stock, if eaten, it is toxic to cattle. For these reasons, in Australia S. obtusifolia is designated as potentially of national concern, and authorities estimate that this invader can lead properties to become unproductive (Weeds of Australia, www.environment.gov.au/cgi-bin/biodiversity/invasive/weeds/weedsearch.pl; Land Protection, www.nrw.qld.gov.au/factsheets/pdf/pest/pp18.pdf). In the flora area, its range of distribution appears to have expanded from five southern and southeastern states in the early 1980s (Florida, Kentucky, Missouri, Texas, and Virginia; Irwin and Barneby) to currently almost half of the states. Although a few specimens were collected as far north as Nebraska and Wisconsin, it is not known to be established in those states.
Senna tora (Linnaeus) Roxburgh (Cassia tora Linnaeus) is sometimes considered synonymous with S. obtusifolia. However, due to differences in length and curvature of the fruit and in length of the petiole and pedicel, B. R. Randell and B. A. Barlow (1998) considered it distinct. H. S. Irwin and R. C. Barneby (1982) observed a range rather than distinct categories in the measures and shapes of these traits, and only molecular phylogenetic and biogeographic studies accompanied by morphometric analyses may definitively solve this taxonomic dilemma.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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