9b. IVESIA Torrey & A. Gray sect. IVESIA
Horkelia Chamisso & Schlechtendal [unranked] Lycopodioides Rydberg; Ivesia [unranked] Lycopodioides (Rydberg) Rydberg; Ivesia sect. Lycopodioides (Rydberg) O. Stevens
Plants usually rosetted or tufted, rarely ± matted (I. pygmaea), not forming hanging clumps (not in vertical rock crevices except I. longibracteata), ± aromatic; taproot stout to fusiform and fleshy. Stems (0.2–)0.3–2(–4) dm. Basal leaves usually loosely to very tightly cylindric (mousetail-like in I. muirii), rarely weakly planar (I. longibracteata); stipules present; leaflets overlapping, individually distinguishable or not, lobed to base, sparsely to densely hairy, sometimes glabrous or glabrate; terminal leaflets indistinct. Cauline leaves (0–)1–3, ˂sometimes paired˃; blade usually ± reduced to vestigial, rarely well developed. Inflorescences usually ± congested, sometimes becoming open in fruit, flowers mostly arranged in 1–few(–several in I. gordonii var. wasatchensis) loose to capitate glomerules. Pedicels remaining straight. Flowers: hypanthium shallowly cupulate or campanulate, sometimes turbinate (I. gordonii); petals not medially reflexed, golden to pale yellow, sometimes white (I. utahensis) and then sometimes pink-tinged, not or scarcely clawed, apex acute to truncate, rounded, or emarginate; stamens 5 (10 in I. pygmaea), anthers longer than wide, laterally dehiscent; carpels (1–)2–15(–30 in I. pygmaea). Achenes vertical, smooth or nearly so, not carunculate.
Species 8 (8 in the flora): w United States.
Species in sect. Ivesia tend to form compact rosettes or tufts in open montane to alpine areas, often where rocky but generally not growing in rock crevices (except Ivesia longibracteata). General characteristics of the section are an overall evident glandularity, loosely to tightly cylindric leaves (mousetail-like in I. muirii), relatively short ascending to erect stems, straight pedicels, and flowers that are typically congested into 1–few capitate clusters that sometimes become more open in fruit. The taproots of some species, especially I. lycopodioides, are markedly enlarged, an adaptation to alpine growing conditions. The inclusion of two anomalous species in the section, I. longibracteata and I. webberi, is tentative; it is also possible that I. cryptocaulis belongs here rather than in sect. Setosae.
Section Ivesia has its center of species diversity in the high Sierra Nevada of California, where Ivesia pygmaea, with its ten stamens and more open habit, is possibly transitional between sects. Ivesia and Setosae. Ivesia gordonii (the most widespread species), I. tweedyi, and I. utahensis form an arc around the northern Great Basin, as outliers from the core Sierran distribution of the section.
Some early floras treated Ivesia pygmaea and I. lycopodioides as varieties of I. gordonii (for example, W. H. Brewer et al. 1876–1880, vol. 1) or Potentilla gordonii (Hooker) Greene (W. L. Jepson [1923–1925], 1909–1943, vol. 2). Recent treatments follow D. D. Keck (1938) in recognizing all three as distinct species; some annotations and references are nevertheless carried over from the earlier expanded circumscription of I. gordonii.
Since Ivesia cryptocaulis is sometimes identified as a member of sect. Ivesia, it is included herein and keys out in the seventh couplet.