Flora of North America species comparison

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Descurainia nelsonii

Nelson's tansy-mustard, sagebrush tansymustard
Habit Annuals; eglandular; sparsely to moderately pubescent, sometimes glabrous distally, not canescent, trichomes dendritic.
Stems

erect, usually branched basally or slightly distally, rarely unbranched, (0.7–)0.9–3.2(–4.5) dm.
Basal leaves

petiole 0.5–1.5 cm;

blade pinnate, ovate or oblong in outline, 0.8–2.5 cm, lateral lobe (2–5 pairs), margins dentate or entire.
Cauline leaves

sessile or shortly petiolate;

blade smaller distally, distal lobes often narrower, sparsely to moderately pubescent.
Racemes

considerably elongated in fruit.
Flowers

sepals ascending, yellowish, oblong, 0.7–1.2 mm, pubescent;

petals narrowly oblanceolate, 0.8–1.2 × 0.2–0.4 mm;

median filaments 1–1.5 mm;

anthers 0.1–0.2 mm.
Fruiting pedicels

divaricate-ascending (often at 20–45º angle), straight, (1.5–)2.5–7(–10) mm.
Fruits

erect or ascending, linear, not or slightly torulose, (0.4–)5–8(–10) × 0.7–1 mm;

valves each with distinct midvein;

septum not veined;

ovules 6–12 per ovary;

style 0.1–0.2 mm, glabrous.
Seeds

uniseriate, brown, oblong, 0.6–0.8 × 0.4–0.5 mm.
2n

= 14.

Descurainia nelsonii
Phenology Flowering late May-mid Jul.
Habitat Roadsides, sagebrush, wash bottoms, silty flats, gravelly grounds
Elevation 800-3000 m (2600-9800 ft)
Distribution
from FNA
CA; ID; MT; NV; OR; WA; WY; BC
[WildflowerSearch map]
[BONAP county map]
Discussion

Descurainia nelsonii was treated by L. E. Detling (1939) and R. C. Rollins (1993) as a subspecies of D. pinnata, but the latter in the sense of these authors is not monophyletic, comprising instead either four or two unrelated species, respectively. ITS molecular data (B. E. Goodson 2007) suggest that D. nelsonii is most closely related to D. longepedicellata and D. paradisa. It can be distinguished from the latter species by its linear fruits with cuneate tips; D. paradisa has obovoid fruits with rounded tips. Descurainia nelsonii resembles D. pinnata subsp. brachycarpa in the orientation of fruiting pedicels and in having short styles (to 0.3 mm) and small seeds (to 1 × 0.5 mm). It differs in being branched (versus simple) at base and in having smaller flowers (petals 0.7–1 versus 1.5–2.6 mm), fewer ovules (6–12 versus 16–40) per ovary, linear (versus subclavate) fruits, and uniseriate (versus biseriate) seeds.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 7, p. 525.
Parent taxa Brassicaceae > tribe Descurainieae > Descurainia
Sibling taxa
D. adenophora, D. brevisiliqua, D. californica, D. incana, D. incisa, D. kenheilii, D. longepedicellata, D. obtusa, D. paradisa, D. pinnata, D. sophia, D. sophioides, D. torulosa
Synonyms Sophia nelsonii, D. brachycarpa var. nelsonii, D. pinnata subsp. nelsonii, D. pinnata var. nelsonii
Name authority (Rydberg) Al-Shehbaz & Goodson: Harvard Pap. Bot. 12: 422. (2007)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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