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northern tansy-mustard

tansy mustard

Habit Annuals or biennials; eglandular or glandular distally; glabrate to moderately pubescent, trichomes dendritic, sometimes mixed with simple ones. Annuals, biennials, or perennials [shrubs, subshrubs]; not scapose; glabrous, glabrate, or sparsely to densely pubescent, trichomes usually short-stalked, dendritic, rarely also simple, sometimes mixed with unicellular, glandular, clavate papillae.
Stems

erect, unbranched or sometimes branched distally, (0.5–)1.5–11(–18) dm.

erect or prostrate, unbranched or branched basally and/or distally.

Leaves

basal and cauline; petiolate or sessile;

basal (often withered by flowering), rosulate, petiolate, blade (1–3-pinnate), margins entire or toothed;

cauline petiolate or sessile, blade often similar to basal.

Basal leaves

petiole 0.5–5 cm;

blade pinnate or, sometimes, 2-pinnate, broadly oblanceolate to ovate in outline, 2.5–11.4(–15.2) cm, lateral lobes lanceolate, (to 10 × 4 mm), margins incised.

Cauline leaves

sessile or shortly petiolate;

blade smaller distally, distal lobes often narrower, surfaces often glabrous or sparsely pubescent.

Racemes

elongated or not in fruit, (flowers overtopped by developing fruits).

(proximally sometimes bracteate), elongated or not in fruit.

Flowers

sepals erect, yellowish, oblong, 1.6–2.7 mm, glabrous;

petals narrowly oblanceolate, 2–2.5 × 0.3–0.6 mm;

median filaments 2.5–3.5 mm;

anthers 0.3–0.4 mm.

sepals erect to spreading, ovate to oblong or linear;

petals usually obovate or oblanceolate, rarely oblong, (shorter to longer than sepals), claw obsolete or distinct, (apex obtuse);

stamens tetradynamous;

filaments not dilated basally;

anthers oblong to ovate, (apex obtuse);

nectar glands confluent, subtending bases of stamens, median glands present.

Fruiting pedicels

divaricate to ascending, (often recurved in age), slender, (3–)4–9(–13) mm.

divaricate or erect, slender.

Fruits

erect to widely spreading, narrowly linear, slightly torulose, (9–)14–30(–34) × 0.6–1.1 mm, (usually terete, rarely slightly flattened, often curved inward);

valves each with obscure midvein;

septum not veined;

ovules 30–62 per ovary;

style obsolete, 0.07–0.3 mm, glabrous.

siliques or silicles, sessile, usually linear, oblong, clavate, or fusiform, rarely ellipsoid or obovoid, smooth or torulose, terete;

valves each often with distinct midvein, usually glabrous, rarely pubescent;

replum rounded;

septum complete or perforated (membranous, not veined or with 1–3 longitudinal veins);

ovules 5–100 per ovary;

style usually absent, rarely distinct;

stigma capitate.

Seeds

uniseriate, light brown, narrowly oblong, 1–1.5 × 0.3–0.5 mm.

uniseriate or biseriate, plump, wingless, oblong or ellipsoid;

seed coat (minutely reticulate), usually mucilaginous when wetted;

cotyledons incumbent.

x

= 7.

2n

= 14.

Descurainia sophioides

Descurainia

Phenology Flowering Jun–Sep.
Habitat Open meadows, eroded peat, roadsides, disturbed and waste sites, rocky outcrops, mining dumps, gravelly grounds, stream banks, gullies
Elevation 0-1000 m (0-3300 ft)
Distribution
from FNA
AK; BC; MB; NT; NU; YT; Asia (Russian Far East, Siberia)
[BONAP county map]
from USDA
North America; Mexico; South America; Eurasia; n Africa; Atlantic Islands (Canary Islands)
[BONAP county map]
Discussion

Species 45–47 (14 in the flora).

Descurainia species are distributed in three major centers: North America (17 species), South America (ca. 20 species), and the Canary Islands (7 species). Excluding D. sophioides, which extends into Siberia from arctic North America, three additional species are found outside those regions: D. kochii (Petri) O. E. Schulz (Caucasus, Turkey), D. sophia (a cosmopolitan weed of Eurasian origin), and D. tanacetifolia (Linnaeus) Prantl (Alps and the Iberian Peninsula).

Descurainia is taxonomically difficult throughout most of the New World, especially the United States. Extensive morphological variation exists within numerous species and many wide-ranging and widely-overlapping taxa appear to intergrade endlessly. Inter- and infraspecific hybridization is probably extensive given the lack of reproductive barriers between the recently evolved New World species, the ready dispersibility of the mucilaginous seeds, and the weedy tendencies of the majority of taxa that readily occupy disturbed habitats. The frequent occurrence of hybrid populations, suggested by the intergrading morphology and widespread polyploidy, is supported by recent molecular evidence (B. E. Goodson 2007). A second factor contributing to the complexity of North American Descurainia is that the number of taxonomically reliable characters is somewhat limited, with a general lack of agreement among various authors on the characters to be emphasized for circumscription of taxa. A taxonomic nightmare has resulted from the recognition of numerous poorly defined species, subspecies, and varieties. Although an extensive molecular systematic study of the genus was recently conducted (Goodson), some relationships and species boundaries remain unclear. Because detailed population-level, morphological, cytological, and molecular studies of North American Descurainia are still needed, this treatment represents an early “pit stop” on the road to full understanding of the complexity in the genus.

The keys and circumscriptions in both L. E. Detling (1939) and R. C. Rollins (1993) are unreliable for the identification of a given collection to an infraspecific taxon. In a genus where interspecific hybridization is so extensive, it is sometimes impossible to identify reliably every single specimen, especially if mature fruits are lacking. Unfortunately, most North American material in major herbaria consists of either specimens without mature fruits or unrecognized hybrids between various taxa. As a consequence, up to 60% of the holdings of Descurainia species in the major North American herbaria are misidentified. Because mature fruits are critical to proper identification, the following key relies primarily on fruiting material.

Almost all taxonomists have used the presence versus absence of glandular papillae as an important character to subdivide a given complex into species, subspecies, varieties, or forms. Both glandular and eglandular forms sometimes occur within a given population of Descurainia incana, D. incisa, D. paradisa, D. pinnata, or D. sophioides. Some authors were inconsistent in according formal recognition to the glandular versus eglandular plants of a given species. For example, R. C. Rollins (1993) treated the glandular and eglandular forms of D. obtusa and D. paradisa, but not of D. incana and D. sophioides, as distinct subspecies; N. H. Holmgren (2005b) recognized such forms as varieties in D. paradisa but not D. incana. Although the presence versus absence of glands appears to be consistent within certain taxa, reliance on the use of glands as a diagnostic character should be applied with extreme caution.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key
1. Fruits sparsely to densely pubescent at least when young
→ 2
1. Fruits glabrous
→ 4
2. Perennials; fruiting pedicels 1.5-3 mm; fruits subappressed to rachises; styles sparsely pubescent; ovules 10-18 per ovary; Wyoming.
D. torulosa
2. Biennials; fruiting pedicels 6-31 mm; fruits not appressed to rachises; styles glabrous; ovules 16-64 per ovary; Arizona, California, Nevada, New Mexico
→ 3
3. Seeds biseriate; ovules 48-64 per ovary; fruits 1-1.3 mm wide; fruiting pedicels 13-31 mm.
D. adenophora
3. Seeds uniseriate; ovules 16-40 per ovary; fruits 0.7-1 mm wide; fruiting pedicels 6-15 mm.
D. obtusa
4. Fruits usually fusiform, obovate, clavate, or broadly ellipsoid, rarely broadly linear (wider distally)
→ 5
4. Fruits linear (sometimes oblong in D. brevisiliqua)
→ 7
5. Fruits usually clavate, rarely broadly linear (wider distally); seeds biseriate; ovules 16-40 per ovary; valves each with distinct midvein.
D. pinnata
5. Fruits fusiform, obovate, or broadly ellipsoid (sometimes clavate in D. paradisa); seeds uniseriate (sometimes biseriate in D. paradisa); ovules 4-12 per ovary; valves each with obscure midvein
→ 6
6. Fruits long-acute basally and apically; styles (0.2-)0.3-0.6(-0.8) mm; stems (1.3-) 2-10.5(-13.5) dm, unbranched basally, branched distally.
D. californica
6. Fruits acute basally, obtuse apically; styles 0.05-0.3 mm; stems (1-)1.5-3.2(-4.1) dm, branched basally and distally.
D. paradisa
7. Perennials (short-lived); stems 0.1-0.15 dm; racemes not elongated in fruit; ovules 4-8 per ovary.
D. kenheilii
7. Annuals or biennials; stems (0.5-)0.9-12(-18) dm; racemes elongated considerably in fruit (sometimes slightly elongated in D. sophioides); ovules 10-62 per ovary (6-12 in D. nelsonii)
→ 8
8. Fruits often strictly appressed to rachises; fruiting pedicels erect to erect-ascending.
D. incana
8. Fruits not appressed to rachises; fruiting pedicels horizontal, divaricate, or ascending
→ 9
9. Leaf blades 2- or 3-pinnate; fruit septums appearing 2- or 3-veined.
D. sophia
9. Leaf blades usually 1-pinnate (rarely 2-pinnate in D. sophioides); fruit septums not veined
→ 10
10. Plants eglandular; fruits 3-8(-10) mm; petals 0.7-1.2 mm; seeds 0.5-0.8 mm
→ 11
10. Plants glandular or eglandular; fruits 8-30(-34) mm; petals 1.7-2.8 mm; seeds 0.9-1.5 mm
→ 12
11. Biennials; stems 6-11 dm, unbranched; ovules 10-28 per ovary; seeds biseriate.
D. brevisiliqua
11. Annuals; stems (0.7-)0.9-3.2(-4.5) dm, usually branched at or near base, rarely unbranched; ovules 6-12 per ovary; seeds uniseriate.
D. nelsonii
12. Flowers overtopped by developing fruits; ovules 30-62 per ovary.
D. sophioides
12. Flowers not overtopped by developing fruits; ovules 14-32 per ovary
→ 13
13. Plants canescent or not; cauline leaf blades: distal segments oblong to lanceolate, or linear, margins dentate, denticulate or entire; fruits straight or strongly curved inward.
D. incisa
13. Plants not canescent; cauline leaf blades: distal segments linear or oblong, margins entire; fruits straight or slightly curved inward.
D. longepedicellata
Source FNA vol. 7, p. 529. FNA vol. 7, p. 518. Authors: Barbara E. Goodson, Ihsan A. Al-Shehbaz.
Parent taxa Brassicaceae > tribe Descurainieae > Descurainia Brassicaceae > tribe Descurainieae
Sibling taxa
D. adenophora, D. brevisiliqua, D. californica, D. incana, D. incisa, D. kenheilii, D. longepedicellata, D. nelsonii, D. obtusa, D. paradisa, D. pinnata, D. sophia, D. torulosa
Subordinate taxa
D. adenophora, D. brevisiliqua, D. californica, D. incana, D. incisa, D. kenheilii, D. longepedicellata, D. nelsonii, D. obtusa, D. paradisa, D. pinnata, D. sophia, D. sophioides, D. torulosa
Synonyms Sisymbrium sophioides, Hesperis arctica, Sisymbrium arcticum, Sophia sophioides Huguenenia, Sophia
Name authority (Fischer ex Hooker) O. E. Schulz: in H. G. A. Engler, Pflanzenr. 86[IV,105]: 316. (1924) Webb & Berthelot: Hist. Nat. Îsles Canaries 3(2,3): 72. (1836)
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