Plants usually tufted or matted (diffusely so in I. cryptocaulis), sometimes rosetted, often forming hanging clumps in vertical rock crevices, ± aromatic; taproot slender or stout, not fusiform or fleshy. Stems (0.1–)0.2–2.5(–3) dm. Basal leaves planar or loosely to tightly cylindric; stipules present; leaflets separate to overlapping, usually individually distinguishable, toothed 1/4–3/4 or lobed to base, rarely entire, sparsely to densely hairy; terminal leaflets distinct or indistinct. Cauline leaves (0–)1–2(–4), not paired; blade well developed to vestigial. Inflorescences open to congested, flowers arranged ± individually (or ± glomerulate in I. paniculata and I. rhypara). Pedicels usually becoming ± curved, often sigmoid. Flowers: hypanthium mostly patelliform, sometimes shallowly cupulate or (in I. arizonica) campanulate or turbinate; petals not medially reflexed, yellow to white, not clawed, apex obtuse to rounded; stamens 5–35(–40), anthers longer or shorter than wide, laterally dehiscent; carpels 1–20(–40). Achenes vertical, usually rugose, sometimes smooth, ± carunculate (except I. cryptocaulis).

Distribution

w United States, nw Mexico.

Discussion

Species 11 (11 in the flora).

The planar-leaved, chasmophytic members of sect. Setosae found in and around the mountains centered on the Mojave Desert are hypothesized to represent the ancestral radiation of Ivesia, on the basis of morphology and distribution. A secondary radiation northward into the Great Basin is characterized by a complete sequence in size reduction, dissection, and increased number of leaflets, paralleled by a reduction in numbers of floral parts. Ivesia saxosa retains the most pleisiomorphies and could readily be accommodated within Potentilla in the strict sense, as has commonly been done. Gross morphology of I. saxosa is nearly identical to that of I. arizonica, which has been treated as a distinct genus, Purpusia, on the basis of its lack of an epicalyx, deep hypanthium, and stipelike torus. The narrow endemic I. patellifera is intermediate between these two species, and an identical habit is shared by I. baileyi and I. jaegeri, which have more dissected leaflets and more reduced flowers. All of these species are now placed in the same genus, either as Ivesia (B. Ertter 1989) or as Potentilla (J. T. Howell 1945).

Most species in sect. Setosae are more or less petrophytic (in contrast to other sections), often growing in crevices of vertical cliffs. The protection offered by these habitats often allows extended blooming periods and resultant indeterminate inflorescences that produce flowers as long as conditions are suitable, including at the height of summer when relatively few other desert species are in bloom. Stems can initially radiate in almost all directions relative to the substrate (vertical in chasmophytes, horizontal in others), but they generally succumb to gravity with increased number of flowers and become either pendent or prostrate. In particularly favorable years, blooming season and flower number can exceed the ranges given here. The small but often numerous flowers are visited by a wide diversity of potential pollinators, including ants, which are attracted to the glistening, nectariferous hypanthial disc. Most species of sect. Setosae have carunculate seeds, which may indicate that ants play a role in seed dispersal, a particularly useful adaptation for chasmophytic plants.

Since Ivesia longibracteata (sect. Ivesia) is sometimes identified as a member of sect. Setosae, it is included herein and keys out in the sixth couplet.

Selected References

None.

Lower Taxa

Ivesia arizonica, Ivesia baileyi, Ivesia callida, Ivesia cryptocaulis, Ivesia jaegeri, Ivesia paniculata, Ivesia patellifera, Ivesia rhypara, Ivesia saxosa, Ivesia setosa, Ivesia shockleyi

Key

1	Basal leaves planar; lateral leaflets (2–)5–20(–25) mm, incised 1/4–3/4 to base into teeth or lobes	> 2
1	Basal leaves ± cylindric to weakly planar; lateral leaflets 0.5–8 mm, incised to base or nearly so into separate lobes, sometimes entire	> 6
2	Stamens 15–35(–40).	Ivesia saxosa
2	Stamens 5–10	> 3
3	Epicalyx bractlets 0(–3); Mojave Desert and n Arizona	> 4
3	Epicalyx bractlets 5; n Great Basin and adjacent mountains	> 5
4	Hypanthia patelliform, 0.5(–1) mm deep; Kingston Range, California.	Ivesia patellifera
4	Hypanthia turbinate or campanulate, 1.5–3(–5) mm deep; se California, s Nevada, and n Arizona.	Ivesia arizonica
5	Lateral leaflets incised 1/4–3/4 to base, lobes not setose apically; basal leaves: sheathing bases not or sparsely strigose abaxially; volcanic substrates.	Ivesia baileyi
5	Lateral leaflets incised ± 3/4 to base, sometimes nearly to base, lobes usually ± setose apically; basal leaves: sheathing bases ± strigose abaxially; usually calcareous substrates.	Ivesia setosa
6	Epicalyx bractlets longer than sepals; inflorescences loosely subcapitate; pedicels remaining straight (Castle Crags, n California).	Ivesia longibracteata
6	Epicalyx bractlets shorter than (or equal to) sepals; inflorescences open to congested, not subcapitate; pedicels usually ± curved in fruit	> 7
7	Stamens 20	> 8
7	Stamens 5	> 9
8	Petals yellow, narrowly oblanceolate; lateral leaflet lobes 3–6; Spring Mountains, Nevada, and Clark Mountain, California.	Ivesia jaegeri
8	Petals white, obovate; lateral leaflets lobes (0–)2–4; San Jacinto Mountains, California.	Ivesia callida
9	Plants grayish; lateral leaflet surfaces densely hirsute, cryptically glandular; inflorescences congested, 5–200-flowered; petals linear to narrowly oblanceolate, 1–1.5 mm, white to pale yellowish; 1300–1900 m	> 10
9	Plants green to grayish green; lateral leaflet surfaces ± sparsely hirsute or loosely long-strigose, evidently glandular; inflorescences ± open to ± congested, 1–20(–30)-flowered; petals oblanceolate to spatulate or narrowly obovate, (1–)1.5–3.2 mm, ± yellow; 1700–4000 m	> 11
10	Leaflet lobes (0–)2–4(–9), elliptic to obovate or orbiculate, 0.5–3(–4) mm; n Nevada, se Oregon.	Ivesia rhypara
10	Leaflet lobes (0–)3–8(–15), elliptic to narrowly obovate, 0.5–2 mm; ne California.	Ivesia paniculata
11	Plants diffusely matted; lateral leaflet surfaces loosely long-strigose; Spring Mountains, s Nevada.	Ivesia cryptocaulis
11	Plants tufted to ± densely matted; lateral leaflet surfaces ± sparsely hirsute; Great Basin and n Sierra Nevada	> 12
12	Lateral leaflets incised ± 3/4 to base, sometimes nearly to base, into ovate teeth to narrowly obovate lobes; usually calcareous substrates.	Ivesia setosa
12	Lateral leaflets incised to base or nearly so into oblanceolate to obovate or elliptic lobes; various substrates, seldom calcareous.	Ivesia shockleyi