Alyssum |
Alyssum desertorum |
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alyssum, madwort |
desert alyssum, desert madwort |
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Habit | Annuals or perennials [biennials, subshrubs]; not scapose; trichomes sessile, stellate, with 2–6 minute basal branches (branches as many as 3–25), rays branched or not, sometimes trichomes simple [lepidote]. | Annuals; canescent throughout except fruit, trichomes appressed, 8–20-rayed. | ||||||||||||||||||||
Stems | erect, ascending, or decumbent, unbranched or branched. |
simple or few to several from base, erect, ascending, or decumbent, (0.2–)0.5–1.8(–2.8) dm. |
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Leaves | basal and cauline; petiolate or sessile; basal rosulate or not, petiolate or sessile, blade margins entire; cauline petiolate or sessile, blade (base cuneate or attenuate), margins entire. |
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Cauline leaves | subsessile or (proximal) attenuate to petiole-like base (to 0.5 cm); blade linear to oblanceolate-linear, (0.3–)0.5–2.5(–3) cm × (0.5–)1–3(–4) mm (gradually smaller distally), base attenuate, apex acute. |
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Racemes | (few- to several-flowered, sometimes corymbose or paniculate). |
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Flowers | sepals ovate or oblong, lateral pair not saccate; petals yellow or white [rarely pink], suborbicular, spatulate, oblanceolate, linear-oblanceolate, or, obovate (apex obtuse or emarginate); stamens tetradynamous; filaments not winged, uni- or bilaterally winged, appendaged, or toothed; anthers ovate or oblong; nectar glands (4), 1 on each side of lateral stamen, median glands absent; (placentation apical or parietal). |
sepals oblong, 1.4–1.8(–2) × 0.4–0.5 mm, stellate-pubescent; petals pale yellow, oblanceolate, 2–2.5 × 0.5–0.6 mm, base attenuate, apex obtuse or retuse, sparsely stellate-pubescent abaxially; filaments: median pairs not toothed, gradually expanded from apex to narrowly winged base, lateral pair with broadly winged appendage apically notched into 2 teeth, 1–1.8(–2) mm; anthers ovate, 0.1–0.2 mm. |
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Fruiting pedicels | ascending, divaricate, or reflexed, slender or stout. |
ascending or subdivaricate, straight, stout, (1–)1.5–3.5(–4.5) mm, trichomes uniformly stellate. |
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Fruits | sessile, ovate-oblong, obovate, or elliptic [obcordate, rarely globose], usually strongly flattened, latiseptate, rarely inflated; valves each not veined (smooth), pubescent or glabrous; replum (visible), rounded; septum complete, (membranous, translucent, veinless); ovules 1 or 2 [or 4–8] per ovary; stigma capitate. |
orbicular, 2.5–4(–4.5) mm diam., apex shallowly emarginate, usually glabrous; valves uniformly inflated at middle, broadly flattened at margins, often glaucous, rarely sparsely pubescent (when young); ovules 2 per ovary; style 0.3–0.7 mm, glabrous. |
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Seeds | biseriate or aseriate, flattened, winged or not, orbicular or suborbicular to ovoid; seed coat (smooth or minutely reticulate), mucilaginous or not when wetted; cotyledons accumbent or incumbent. |
ovoid, slightly compressed, 1.2–1.5 × 0.9–1.1 mm, margined or not. |
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2n | = 32. |
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Alyssum |
Alyssum desertorum |
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Phenology | Flowering Apr–Jul. | |||||||||||||||||||||
Habitat | Deserts, rocky areas, disturbed sites, roadsides, fields, meadows, sagebrush flats | |||||||||||||||||||||
Elevation | 800-2000 m (2600-6600 ft) | |||||||||||||||||||||
Distribution |
North America; se Europe; Asia; n Africa |
CA; CO; ID; MT; ND; NE; NV; OR; SD; UT; WA; WY; AB; BC; SK; Europe; c Asia [Introduced in North America]
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Discussion | Species ca. 170 (6 in the flora). Alyssum has five introduced and one native species in North America. It is taxonomically difficult and is centered in Turkey and adjacent countries. For the determination of most species, both flowers and mature fruits are needed. Alyssum has been split into nine or more segregates; the segregates are based on the presence of staminal appendages, petal color, and number of ovules per ovary. In the absence of thorough molecular studies on Alyssum and its immediate relatives, it is more practical to delimit the genus broadly, as done here. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 7, p. 247. | FNA vol. 7, p. 248. | ||||||||||||||||||||
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Name authority | Linnaeus: Sp. Pl. 2: 650. (1753): Gen. Pl. ed. 5, 293. (1754) | Stapf: Denkschr. Kaiserl. Akad. Wiss., Wien. Math.-Naturwiss. Kl. 51: 302. (1886) | ||||||||||||||||||||
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