Herbs, perennial, rosetted, tufted, or matted, sometimes forming hanging clumps, often aromatic, (0.1–)0.3–6(–6.5) dm, sparsely to densely hirsute, sericeous, villous, or pilose, sometimes glabrate, sparsely to densely glandular-puberulent to stipitate-glandular; caudices simple or branched, branches usually relatively short, rarely elongate (I. cryptocaulis), taproot slender to stout, sometimes fusiform and fleshy. Stems (1–)2–20+, prostrate or pendent to erect, green, grayish, or reddish. Leaves winter-marcescent, primarily basal, cauline 0–10(–15), well developed to vestigial, usually alternate (cauline opposite in I. muirii, I. webberi), odd-pinnate; stipules persistent, sometimes absent, basally adnate to petiole, linear to lanceolate or elliptic, margins usually entire, cauline sometimes lobed; petiole present; blade narrowly oblong to filiform, planar to cylindric, 0.5–20(–25) cm, foliaceous, leaflets (3–)7–161, sometimes separate, more often overlapping at least distally, sometimes tightly imbricate, terminal distinct or, more often, confluent with distalmost lateral ones, ovate or obovate to orbiculate or ± flabellate, often oriented in 3-dimensions, leaflet arrangement appearing verticillate, margins flat, palmately incised from 1/4 to completely to base into teeth or linear or oblanceolate to oval or obovate lobes, venation palmate. Inflorescences terminal, (1–)3–100(–250)-flowered, ± cymes, open or of 1–several loose to capitate glomerules; bracts present, reduced; bracteoles absent. Pedicels present, straight to sigmoid. Flowers 4–15 mm diam.; epicalyx bractlets (0–)5; hypanthium patelliform to campanulate or cupulate to turbinate, 0.5–3(–4) mm; sepals 5 (usually 4 in I. campestris), spreading, lanceolate to broadly ovate or deltate; petals 5 (usually 4 in I. campestris), golden to pale yellow to white, sometimes pink-tinged (red in I. multifoliolata), linear or narrowly oblanceolate to obovate, sometimes obcordate; stamens 5–20(–40), usually shorter than petals; filaments not forming tube; torus ± flat to conic, or turbinate (in sect. Comarella), rarely elongate and stipelike (I. arizonica); carpels 1–20(–40), glabrous, styles subterminal, usually ± filiform, sometimes rough-thickened proximally; ovule 1. Fruits aggregated achenes, individually deciduous, 1–20+, obliquely ovoid to reniform, 0.8–3 mm, sometimes rugose and/or carunculate, glabrous; hypanthium persistent; sepals persistent, erect; styles tardily deciduous, jointed. x = 7.
w United States, nw Mexico.
Species 30 (30 in the flora).
The often aromatic (resin-scented) ivesioid genera (Horkelia, Horkeliella, and Ivesia) have generally been assumed to be derived from Potentilla in the broad sense, an interpretation confirmed by molecular analyses (T. Eriksson et al. 1998, 2003; C. Dobeš and J. Paule 2010; M. H. Töpel et al. 2012). Continued recognition of the three genera (and Duchesnea) accordingly creates a paraphyletic Potentilla; the senior author does not accept the dictum that paraphyletic groups are inherently unnatural and finds it more useful to continue recognizing the ivesioid genera as here circumscribed.
In spite of the morphologic and ecologic extremes encompassed within Ivesia, spanning the continuum from planar-leaved desert chasmophytes to alpine species with mousetail-like leaves, molecular phylogenetic analyses of representatives from all sections of Ivesia, Horkelia, and Horkeliella result in a monophyletic near-polytomy, indicating rapid morphologic radiation not matched by molecular divergence (C. Dobeš and J. Paule 2010; M. H. Töpel et al. 2012). This interpretation is not fully supported by M. Töpel et al., but until the lack of concordance between molecular-based clades and even the most well-defined morphology-based groups is addressed, any conclusions based on molecular analysis alone are inconclusive.
The hypothesis on which the sequence of species used here is based is that the ivesiod genera represent a threshold-crossing radiation in response to the late Tertiary development of xeric conditions in western North America, with adaptations that allow drought-avoidance or minimize water loss. A recurrent trend is the progressive reduction in size and number of floral parts occurring independently in multiple lineages. The end product is a flower in which the nectariferous, patelliform hypanthium itself becomes the main pollinator attractor. Much of this evolutionary radiation has occurred in the various island-like habitats that characterize the arid West, with the result that the ivesioid genera include a high percentage of narrowly endemic species.
In the following descriptions, stems refer to flowering stems, with length including the inflorescence. For chasmophytic (growing on cliffs) species in sect. Setosae, terms such as decumbent are in reference to the vertical rock face. The inflorescence is composed of the branched portion of the flowering stem, including the proximalmost branched node. Cauline leaves are on the portion of the flowering stem proximal to the inflorescence. Planar leaves are those in which the leaflets are largely arranged in a single plane on both sides of the rachis; in cylindric leaves the lobes of deeply incised leaflets are arranged evenly around the rachis and thus appear verticillate. Well-developed blades of cauline leaves are similar to those of basal leaves, though progressively reduced distally; vestigial blades are reduced to a simple lobe, which, with the stipules, has the appearance of a 3-lobed bract. Leaf incisions are referred to as teeth if less than half to base, as lobes if more than half. Counts of leaflet lobes are of ultimate segments, including teeth, not just of primary segments incised to the base or nearly so. Inflorescence structure is described at peak anthesis; at early anthesis flowers are often more congested than indicated here and sometimes become more distant in fruit. Pedicels at proximal nodes are often significantly longer than others; those in most sections remain more or less straight in fruit or bend proximal to the flower, in contrast to those of sect. Setosae that generally become strongly curved or even sigmoid. Petal color is described at peak of flowering; yellow petals often fade afterward. Vestiture descriptions are primarily of non-glandular hairs; subsessile glands or evidently septate-glandular trichomes are universal in Ivesia, though often sparse or hidden by dense non-glandular vestiture.
Key to sections of Ivesia
|1||Pedicels usually becoming ± curved, often sigmoid; basal leaves planar or loosely to tightly cylindric, leaflets separate to overlapping, toothed 1/4–3/4 or lobed to base; achenes often rugose, ± carunculate (except I. cryptocaulis); flowers arranged ± individually (or ± glomerate in I. paniculata and I. rhypara); plants usually ± petrophytic, often forming hanging clumps in vertical rock crevices.||Ivesia sect. Setosae|
|1||Pedicels remaining ± straight; basal leaves loosely to tightly cylindric (sometimes weakly planar in I. longibracteata), leaflets ± overlapping, lobed to base (except I. multifoliolata); achenes smooth, not carunculate; flowers arranged individually or in 1–several loose to capitate glomerules; plants usually not petrophytic (except I. longibracteata), not forming hanging clumps||> 2|
|2||Stamens 5; petals not or scarcely clawed||> 3|
|2||Stamens 10–20; petals often clawed||> 4|
|3||Inflorescences usually ± congested, sometimes becoming open in fruit, flowers arranged in 1+ loose to capitate glomerules; hypanthia shallowly cupulate or campanulate, sometimes turbinate; petals usually narrowly oblanceolate or spatulate to broadly obovate, sometimes linear, not medially reflexed, usually yellow, sometimes white (I. utahensis); stems (0.2–)0.3–2(–4) dm.||Ivesia sect. Ivesia|
|3||Inflorescences open, flowers arranged individually; hypanthia patelliform; petals linear to oblanceolate or narrowly elliptic, medially reflexed, yellow or red; stems (1.8–)2–6(–6.5) dm.||Ivesia sect. Comarella|
|4||Cauline leaves (0–)1; stems 0.3–1(–1.5) dm; petals golden yellow.||Ivesia sect. Ivesia|
|4||Cauline leaves (1–)2–10(–15); stems (0.3–)1–4.5(–5.5) dm; petals light yellow to white, sometimes pink-tinged||> 5|
|5||Basal leaves not mousetail-like, loosely to tightly cylindric, individual leaflets distinguishable, sparsely to densely hairy or glabrate.||Ivesia sect. Unguiculatae|
|5||Basal leaves mousetail-like, tightly to very tightly cylindric, individual leaflets not or scarcely distinguishable, densely hairy||> 6|
|6||Stamens 20; carpels (1–)2–20; inflorescences: flowers arranged individually and/or in glomerules; anthers white to yellowish, ± as long as to longer than wide.||Ivesia sect. Unguiculatae|
|6||Stamens 15; carpels 1; inflorescences: flowers arranged individually; anthers purple, shorter than wide.||Ivesia sect. Stellariopsis|