Descurainia sophia
Descurainia brevisiliqua
fine-leaf tansy-mustard, fixweed, flixweed, flixweed tansymustard, herb sophia, not much flower, tansy mustard
erect, unbranched or branched distally, (1–)2–7(–10) dm.
erect, unbranched basally, branched distally, 6–11 dm.
petiole 0.1–2(–3) cm;
blade 2- or 3-pinnate, ovate or oblong to obovate in outline, to 15 cm, lateral lobes linear or oblong, (to 10 × 2 mm), margins entire.
petiole 0.5–1.5 cm;
blade pinnate, oblanceolate to obovate or ovate in outline, 1–5 cm, lateral lobes (2–5 pairs), linear, margins entire or serrate to incised (apex obtuse).
sessile or shortly petiolate;
blade smaller distally, distal lobes often narrower, surfaces often glabrous.
sessile or shortly petiolate;
blade smaller distally, distal lobes often narrower, surfaces densely pubescent.
considerably elongated in fruit.
(paniculate, often with short branches), considerably elongated in fruit.
sepals erect to ascending, yellowish, oblong, 1.8–2.8 mm, glabrate to sparsely pubescent;
petals narrowly oblanceolate, 2–3 × 0.4–0.6 mm;
median filaments 2–3 mm;
anthers 0.3–0.4 mm.
sepals spreading, yellowish, oblong, 1.4–2 mm, pubescent, (trichomes dendritic, sometimes mixed with simple ones);
petals oblanceolate, 0.7–1 × 0.1–0.2 mm;
median filaments 1.5–2 mm;
anthers 0.2–0.3 mm.
divaricate to ascending, straight, (5–)8–15(–20) mm.
divaricate-ascending, straight, 4–7(–11) mm.
divaricate-ascending to erect, narrowly linear, torulose, (12–)15–27(–30) × 0.5–0.8(–1) mm, (straight or curved upward);
valves each with distinct midvein;
septum with a broad central longitudinal band appearing as 2 or 3 veins;
ovules 20–48 per ovary;
style obsolete, 0.05–0.2 mm, glabrous.
divaricate to erect, linear to oblong, not torulose, 3–8(–10) × 1–1.2 mm;
valves each with distinct midvein;
septum not veined;
ovules 10–28 per ovary;
style obsolete to 0.1 mm, glabrous.
uniseriate, reddish brown, oblong, 0.7–1.3 × 0.3–0.6 mm.
biseriate, light brown, ellipsoid, 0.5–0.7 × 0.3–0.4 mm.
= 28.
= 42.
Descurainia sophia
Descurainia brevisiliqua
Deviant chromosome counts (e.g., 2n = 12, 14, 20, 38; see R. C. Rollins 1993, N. H. Holmgren 2005b, S. I. Warwick and I. A. Al-Shehbaz 2006) are most certainly erroneous, and the species appears to be exclusively tetraploid based on x = 7.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
R. C. Rollins (1993) reduced Descurainia brevisiliqua to synonymy of the diploid D. obtusa. This hexaploid species differs from the latter in having biseriate (versus uniseriate) seeds and glabrous (versus densely to moderately pubescent) fruits. Molecular data (B. E. Goodson 2007) show that it is consistently separate from, and unrelated to, D. obtusa, instead being affiliated with D. incana and D. incisa. Descurainia brevisiliqua differs from the latter two species by having biseriate (versus uniseriate) seeds and oblong, non-torulose fruits that, unlike those of D. incana, are not appressed to rachises. Although the fruits of D. brevisiliqua resemble those of some D. pinnata subspecies, it can be readily distinguished from the latter by its tall, strict growth habit with numerous short branches in the distal part of the plant, more linear leaf segments, stems that are usually purple, and late–summer flowering period.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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