Streptanthus
J. Acad. Nat. Sci. Philadelphia 5: 134, plate 7. 1825.
Annuals, biennials, or perennials; (short-lived, caudex poorly developed, usually not woody); not scapose; glabrous or pubescent. Stems usually erect, rarely ascending, unbranched or branched, (often glaucous, glabrous distally). Leaves basal and cauline; petiolate or sessile; basal rosulate or not, petiolate or sessile, blade margins entire or dentate to lyrate-pinnatifid; cauline usually sessile, rarely petiolate, blade (base usually auriculate or amplexicaul), margins entire or dentate, pinnatifid, or pinnatisect. Racemes (rarely with a terminal cluster of sterile flowers, usually ebracteate, sometimes bracteate), usually elongated in fruit. Fruiting pedicels usually divaricate-ascending, rarely erect or suberect, slender or stout. Flowers (sometimes zygomorphic); sepals erect, (calyx often urceolate or campanulate), both pairs often saccate basally; petals white, yellow, pink, purple, or brownish, oblong to ovate, (narrow and margins crisped or channeled, or broad and margins neither crisped nor channeled), claw poorly differentiated from blade or distinct, (apex rounded); stamens usually in 3 unequal pairs, rarely tetradynamous; filaments not dilated basally, (adaxial pair longest, frequently connate and anthers sterile or partially sterile, sometimes all filaments distinct and all anthers fertile); anthers linear to oblong; nectar glands confluent. Fruits subsessile or shortly stipitate, linear, torulose or smooth, usually latiseptate, rarely subterete (flattened); valves each with prominent or obscure midvein, usually glabrous, rarely pubescent; replum rounded; septum complete; ovules (10–)12–120 per ovary; style distinct or obsolete; stigma entire or 2-lobed. Seeds uniseriate, usually flattened, rarely plump, usually winged, rarely not winged, oblong, ovoid, orbicular, or suborbicular; seed coat (smooth or minutely reticulate), not mucilaginous when wetted; cotyledons usually accumbent, rarely obliquely so.
Distribution
c, w United States, n Mexico.
Discussion
Species ca. 35 (35 in the flora).
The infrageneric taxonomy of Streptanthus is somewhat controversial. W. L. Jepson (1909–1943, vol. 2) united it with Caulanthus and divided the combined genus into four subgenera, whereas J. E. Rodman et al. (1981) and A. R. Kruckeberg and J. L. Morrison (1983) recognized subgenera and sections. In the absence of comprehensive phylogenetic studies on the entire complex, I prefer not to recognize any infrageneric taxa.
Streptanthus includes species endemic to serpentine soils. Extensive experimental and molecular studies were conducted on the S. glandulosus complex (e.g., A. R. Kruckeberg 1957; M. S. Mayer and P. S. Soltis 1994, 1999; Mayer et al. 1994) and on the nickel hyperaccumulators (e.g., R. D. Reeves et al. 1981; Kruckeberg and Reeves 1995); the taxonomy of that complex has not yet been satisfactorily resolved.
In the following descriptions, characteristics described for basal leaves also apply to those of juvenile perennial plants. Measurements of floral parts are made from flowers in the proximal portion of racemes; flower size decreases distally, and distal and late-season flowers are often smaller than those of the proximal or early-season flowers. Measurements of fruiting pedicels and fruits are taken from proximalmost ones. Seed width measurements include the seed wing.
Selected References
None.
Lower Taxa
Key
| 1 | Cauline leaves usually petiolate, rarely sessile, blades with bases not auriculate, sagittate, or amplexicaul | > 2 |
| 1 | Cauline leaves sessile, blades with bases auriculate, sagittate, or amplexicaul | > 6 |
| 2 | Middle cauline leaf blades: margins runcinate- or lyrate-pinnatifid; fruits 3.5-5 mm wide | > 3 |
| 2 | Middle cauline leaf blades: margins entire or repand; fruits 1.2-3.2(-3.5) mm wide | > 4 |
| 3 | Stems glabrous proximally; petals unequal (abaxial pair 5-6 mm, adaxial pair 15- 26 mm); stamens in 3 unequal pairs; styles 0.2-0.5 mm. | Streptanthus cutleri |
| 3 | Stems pilose proximally; petals equal (4-8 mm); stamens tetradynamous; styles 0.5-2.7 mm. | Streptanthus petiolaris |
| 4 | Perennials; middle cauline leaves spatulate-obovate to suborbicular; filament pairs distinct; fruits 2.5-3.2(-3.5) mm wide. | Streptanthus howellii |
| 4 | Annuals; middle cauline leaves usually linear to linear-lanceolate, rarely oblanceolate; filament pairs connate; fruits 1.2-2 mm wide | > 5 |
| 5 | Calyces urceolate; petals 6-9 mm; ovules 22-38 per ovary; California. | Streptanthus barbiger |
| 5 | Calyces campanulate; petals 13-20 mm; ovules 90-120 per ovary; Arkansas, Kansas, Louisiana, Oklahoma, Texas. | Streptanthus hyacinthoides |
| 6 | Racemes bracteate throughout or partly | > 7 |
| 6 | Racemes ebracteate throughout | > 14 |
| 7 | Racemes bracteate throughout or proximalmost flowers bracteate; Texas | > 8 |
| 7 | Racemes bracteate below or between proximalmost 1 or 2 flowers; California, Nevada, Oregon | > 9 |
| 8 | Petals 14-19 mm; stamens tetradynamous; fruits 8-14.5 cm × 2.5-4 mm; ovules 48-80 per ovary; styles 1-3.5 mm. | Streptanthus bracteatus |
| 8 | Petals 16-27 mm; stamens in 3 unequal pairs; fruits 4-9.5 cm × 4.5-6 mm; ovules 26-42 per ovary; styles 0.5-2 mm. | Streptanthus platycarpus |
| 9 | Basal leaf blades pectinate, 1- or 2-pinnatifid, or pinnatisect; fruits smooth or slightly torulose | > 10 |
| 9 | Basal leaf blades not pectinate, pinnatifid, or pinnatisect (not lobed); fruits torulose | > 12 |
| 10 | Middle cauline leaf blades pectinate or pinnatisect into filiform segments, bases not auriculate; fruits geniculately reflexed. | Streptanthus diversifolius |
| 10 | Middle cauline leaf blades usually not lobed, rarely pinnatifid, not forming filiform segments, bases auriculate; fruits usually ascending or divaricate, rarely reflexed | > 11 |
| 11 | Petals white (veins violet); fruits 6-12 cm × 1.7-2.5 mm, valves each with prominent midvein; ovules 60-100 per ovary; seeds 2-2.5 × 1.5-2 mm. | Streptanthus farnsworthianus |
| 11 | Petals rose-purple; fruits 2-5 cm × 1.2-1.7 mm, valves each with obscure midvein; ovules 22-38 per ovary; seeds 1-1.5 × 0.7-0.9 mm. | Streptanthus fenestratus |
| 12 | Annuals; sepals 4-5 mm; fruiting pedicels not expanded at receptacles. | Streptanthus gracilis |
| 12 | Biennials or perennials (short-lived); sepals 6-10(-13) mm; fruiting pedicels expanded at receptacles | > 13 |
| 13 | Cauline leaf blades linear-lanceolate; filaments: adaxial pair connate, 13-16 mm, lateral pair 7-9 mm; Trinity County, California. | Streptanthus oblanceolatus |
| 13 | Cauline leaf blades oblong to obovate or suborbicular; filaments: adaxial pair distinct, (5-)7-11 mm, lateral pair (1.5-)3-5 mm; California, Nevada, Oregon. | Streptanthus tortuosus |
| 14 | Racemes with terminal cluster of sterile flowers; fruit valves sparsely to densely hirsute or hispid | > 15 |
| 14 | Racemes without terminal cluster of sterile flowers; fruit valves glabrous (sometimes hirsute in S. glandulosus) | > 17 |
| 15 | Petals purple (with dark purple veins), claws narrower than blades; fruits 1.3-2.5 cm × 2.5-3.5 mm; seeds not winged; Santa Clara County, California. | Streptanthus callistus |
| 15 | Petals purple (with white margins), purplish white, lemon-yellow, or yellowish white, claws as wide as or wider than blades; fruits 3.5-11.4 cm × 1.5-2.5 mm; seeds winged (wings continuous); Contra Costa, Fresno, Merced, Monterey, San Benito counties, California | > 16 |
| 16 | Middle cauline leaf blade bases not auriculate; filaments: abaxial pair connate; Mt. Diablo, Contra Costa County, California. | Streptanthus hispidus |
| 16 | Middle cauline leaf blade bases auriculate; filaments: abaxial pair distinct; Fresno, Merced, Monterey, San Benito counties, California. | Streptanthus insignis |
| 17 | Perennials, with woody caudex (except S. campestris); calyces ± campanulate; filaments: adaxial pair distinct; anthers 2.5-5 mm, adaxial pair fertile | > 18 |
| 17 | Annuals or biennials, without woody caudex; calyces often urceolate, sometimes campanulate; filaments: adaxial pair often connate, sometimes distinct; anthers 1-6 mm, adaxial pair often sterile, sometimes fertile | > 23 |
| 18 | Cauline leaves overlapping, not smaller distally; petals with darker veins, margins slightly crisped. | Streptanthus barbatus |
| 18 | Cauline leaves not overlapping, smaller distally; petals without darker veins, margins not crisped | > 19 |
| 19 | Fruits descending, arcuate; petals purple or brownish with yellow-green claws. | Streptanthus longisiliquus |
| 19 | Fruits spreading, divaricate-ascending, or ascending, straight or slightly curved; petals uniformly white, maroon-purple, or brownish, rarely claws yellow (S. campestris) | > 20 |
| 20 | Petals: claws white or pale yellow; stamens tetradynamous or nearly so; fruit valves each with obscure midvein | > 21 |
| 20 | Petals: claws purplish; stamens in 3 unequal pairs; fruit valves each with prominent midvein | > 22 |
| 21 | Plants with woody caudex (elevated); stems 2.5-8.6 dm; racemes lax in bud; sepals pale yellow to white; stigmas subentire. | Streptanthus bernardinus |
| 21 | Plants without woody caudex; stems (2.5-)6-15(-18) dm; racemes dense in bud; sepals purple; stigmas 2-lobed. | Streptanthus campestris |
| 22 | Basal leaf blades: margins dentate, petioles broadly winged; fruits (2.5-)3-6(-7) mm wide; stigmas slightly to strongly 2-lobed; ovules 20-38(-46) per ovary; seeds 2.5-5 × 2.2-5 mm. | Streptanthus cordatus |
| 22 | Basal leaf blades: margins entire, petioles usually not winged, rarely narrowly winged; fruits 2-2.7(-3) mm wide; stigmas entire; ovules (42-)48-60 per ovary; seeds 2-2.5(-2.7) × 1.5-2 mm. | Streptanthus oliganthus |
| 23 | Calyces usually campanulate, rarely urceolate; filaments: adaxial pair distinct; anthers: adaxial pair fertile; stigmas strongly 2-lobed | > 24 |
| 23 | Calyces urceolate; filaments: adaxial pair connate; anthers: adaxial pair sterile; stigmas entire or subentire | > 27 |
| 24 | Stamens in 3 unequal pairs; fruits 4.5-6 mm wide; ovules 26-54 per ovary; seeds 3-5 mm wide | > 25 |
| 24 | Stamens tetradynamous; fruits 2-3 mm wide; ovules 54-92 per ovary; seeds 1-1.3 mm wide | > 26 |
| 25 | Petals creamy white (with purple veins) or purple with white margins, 14-18 mm, margins crisped, 1-1.5 mm wide; fruit valves each with obscure midvein; Arizona, New Mexico, Texas. | Streptanthus carinatus |
| 25 | Petals lavender or purplish lavender, 16-27 mm, margins not crisped, 6-9 mm wide; fruit valves each with prominent midvein; Texas. | Streptanthus platycarpus |
| 26 | Sepals glabrous, lateral pairs usually without, rarely with, subapical callus, 0.1-0.3 mm. | Streptanthus maculatus |
| 26 | Sepals hirsute, lateral (and median) pairs with subapical callus, 1-2 mm. | Streptanthus squamiformis |
| 27 | Replums constricted between seeds | > 28 |
| 27 | Replums not constricted between seeds (straight) | > 30 |
| 28 | Annuals; basal leaves not rosulate, blade not mottled; sepals green; petals without darker veins. | Streptanthus vernalis |
| 28 | Biennials; basal leaves rosulate, blade mottled; sepals rose-purple, yellow, or violet; petals with darker veins | > 29 |
| 29 | Stems 1.4-5(-6) dm, usually branched basally, rarely unbranched; petals whitish, abaxial pairs with purple spot, adaxial pairs with faint purple veins; fruit valves each with obscure midvein. | Streptanthus brachiatus |
| 29 | Stems (2.5-)6.5-12(-15) dm, unbranched or paniculately branched distally; petals creamy white, abaxial and adaxial pairs with brownish purple veins; fruit valves each with prominent midvein. | Streptanthus morrisonii |
| 30 | Sepals: abaxial ovate-cordate, lateral ovate-lanceolate, adaxial pair suborbicular to broadly ovate-cordate (forming a bannerlike hood), adaxial pair distinctly larger than abaxial and lateral sepals; fruits pendent. | Streptanthus polygaloides |
| 30 | Sepals: all lanceolate to broadly ovate (not forming a bannerlike hood), subequal; fruits usually erect, ascending, divaricate, or spreading (rarely reflexed in S. glandulosus) | > 31 |
| 31 | Middle cauline leaf blades orbicular or orbicular-ovate, strongly overlapping; fruits strongly falcate. | Streptanthus drepanoides |
| 31 | Middle cauline leaf blades ovate, oblanceolate, lanceolate, or linear, not overlapping; fruits straight, curved, or arcuate | > 32 |
| 32 | Plants usually hirsute basally, rarely glabrous; petals with crisped margins; fruit valves each with prominent midvein, glabrous or sparsely to moderately hirsute. | Streptanthus glandulosus |
| 32 | Plants glabrous basally; petals without crisped margins; fruit valves each with obscure midvein, glabrous | > 33 |
| 33 | Basal leaf blades: margins entire; middle cauline leaf blades linear to narrowly linear-lanceolate; petals 2-3 mm wide. | Streptanthus vimineus |
| 33 | Basal leaf blades: margins usually dentate (S. breweri sometimes entire); middle cauline leaf blades ovate or lanceolate; petals 1-2 mm wide | > 34 |
| 34 | Petals: abaxial pair purplish; filaments: adaxial pair 5-6 mm; fruits 1.3-3 cm; ovules 12-22 per ovary. | Streptanthus batrachopus |
| 34 | Petals: abaxial pair white (with purple veins); filaments: adaxial pair 6-10 mm; fruits 3-9 cm; ovules 24-54 per ovary | > 35 |
| 35 | Foliage green; rachises straight; petals 8-12 mm; fruits strongly arcuate (recurved). | Streptanthus breweri |
| 35 | Foliage mostly yellowish; rachises flexuous; petals 6-8 mm; fruits usually nearly straight, rarely arcuate. | Streptanthus hesperidis |