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Mentzelia involucrata var. megalantha I. M. Johnston

Plants 7–35(–45) cm. Basal leaves: petioles present or absent; blade lanceolate, to 10(–16) cm; margins shallowly to deeply lobed, lobes acute. Cauline leaves: petioles absent; blade ovate to lanceolate, to 10(–16) cm, base often cordate-clasping, margins deeply to shallowly lobed, lobes acute. Bracts white with green margins, conspicuous, concealing pedicel, ovary, and capsule. Flowers: petals white to pale yellow, usually with orange veins, obovate, 13–65 mm, apex mucronate; stamens 4–26 mm, less than 1/2 petal length, all fertile, none petaloid (flowers appearing to have 5 petals); filaments ± monomorphic, linear, distally 2-lobed, lobes 0.5–2 mm; anther stalk shorter or longer than filament lobes; style 8–30 mm. Capsules cylindric to cup-shaped, 14–25(–30) × 5–10 mm, erect. Seeds usually constricted proximal to middle; seed coat anticlinal cell walls wavy. 2n = 18.

Flowering Jan–May. Washes, fans, slopes, desert scrub; 50–900 m; Ariz., Calif.; Mexico (Baja California, Sonora).

Mentzelia involucrata is easily distinguished from other species in sect. Bicuspidaria by its large white bracts, which are strikingly similar to those of M. congesta in sect. Trachyphytum. Phylogenetic studies show that these species are not closely related, suggesting a homoplasious origin of the characteristic (J. M. Brokaw and L. Hufford, 2010). Populations exhibiting petals longer than 3 cm have previously been called var. megalantha. However, a study by G. S. Daniels (1970) suggested that insufficient geographic and morphological discontinuities exist for recognition of varieties.

P. A. Munz (1974) mistakenly cited var. megalantha as Mentzelia involucrata subsp. megalantha I. M. Johnston, a name never validly published.