Herbs [subshrubs or shrubs], annual or perennial. Leaves: basal rosette absent, proximalmost internodes 10+ mm; blade, at least some, with broad basal lobes, margins entire, toothed, or crenate, flat. Flowers: stamens all fertile; filaments monomorphic, filiform, or heteromorphic, outer dorsiventrally flattened, spatulate [linear or lanceolate], not petaloid, inner filiform, unlobed; ovules (and seeds) oriented parallel to long axis of ovary. Capsules usually subcylindric, clavate, lingulate, or funnelform, sometimes ovoid, straight or curved. Seeds oblong, ovoid, or pyriform, dorsiventrally flattened to trigonal, not winged; seed coat cells oblong, much longer than wide, anticlinal walls sinuous.

Distribution

North America, Mexico, West Indies, Central America, South America.

Discussion

Species ca. 23 (7 in the flora).

Reports of Mentzelia hispida Willdenow from Texas (for example, by B. L. Turner et al. 2003) appear to be misidentifications; M. hispida is regarded here as limited to Mexico (see R. McVaugh 2001c), although its distribution approaches the southwestern border of the United States.

In the descriptions that follow, stem length is measured to the first terminal flower.

Selected References

None.

Lower Taxa

Mentzelia aspera, Mentzelia asperula, Mentzelia floridana, Mentzelia isolata, Mentzelia lindheimeri, Mentzelia oligosperma, Mentzelia pachyrhiza

Key

1	Capsule bases rounded or cuneate, capsules and pedicels well-differentiated; fruiting pedicels less than 1 mm diam.	> 2
2	Stamen filaments heteromorphic, 5 outermost narrowly spatulate, inner filiform.	Mentzelia floridana
2	Stamen filaments monomorphic, filiform.	Mentzelia lindheimeri
1	Capsule bases tapering gradually, capsules and pedicels not well-differentiated; fruiting pedicels absent or more than 1 mm diam.	> 3
3	Plants perennial, with caudices or tubers; seeds (1–)2–3(–4) per capsule; petals hairy abaxially on distal 1/2.	> 4
4	Petioles to 3 mm in proximal leaves, absent in distal leaves; capsule walls thick, woody; seeds without transverse folds; plants with caudices.	Mentzelia oligosperma
4	Petioles mostly 3–20 mm, less than 3 mm only on smallest, distalmost leaves; capsule walls thin, brittle; seeds with transverse folds; plants with tubers.	Mentzelia pachyrhiza
3	Plants annual, without caudices or tubers; seeds 5–12 per capsule; petals hairy on apex or abaxially near or at apex.	> 5
5	Stamen filaments monomorphic, filiform; leaf blades to 4.5 × 3.5 cm.	Mentzelia asperula
5	Stamen filaments heteromorphic, 5 outermost slightly to narrowly spatulate, inner filiform; leaf blades to 14–18 × 4.5–10 cm.	> 6
6	Stamens 20–30; fruiting pedicels 1–3 mm.	Mentzelia aspera
6	Stamens 8–12; fruiting pedicels 0.5–0.8 mm.	Mentzelia isolata