Horkelia
Rosaceae tribe Potentilleae
horkelia
1–10+, decumbent to erect, rarely prostrate, green, reddish, or stramineous.
marcescent or winter-persistent, primarily basal, cauline 1–6(–10), gradually or abruptly reduced distally, alternate, odd-pinnate;
stipules persistent, basally adnate to petiole, linear to lanceolate or elliptic, margins entire or pinnately divided into linear to filiform segments;
petiole present;
blade oblanceolate-oblong to linear in outline, planar to cylindric, (1–)2–30(–40) cm, foliaceous, leaflets (3–)5–41, separate or congested and overlapping, terminal usually ± confluent with distalmost lateral ones, elliptic-oblong to ovate or flabellate in outline, margins flat, shallowly toothed to deeply divided into oblanceolate lobes, sometimes nearly entire except for 3-toothed apex, rarely completely entire, venation palmate to pinnate.
alternate, rarely opposite, pinnately (palmately) compound (simple in Alchemilla, Aphanes, and Chamaerhodos);
stipules persistent (absent in Chamaerhodos), adnate to petiole;
venation pinnate or palmate.
terminal, 3–200-flowered, open to congested cymes, flowers arranged individually, in corymbiform clusters, and/or in ± globose glomerules, these sometimes capitate;
bracts present at proximal nodes, ± leafy, becoming reduced distally;
bracteoles absent.
present, usually straight in fruit, sometimes reflexed or recurved.
4–17 mm diam.;
epicalyx bractlets 5;
hypanthium ± cupulate with flattened bases, 1–5.5 mm, less than 1/2 to nearly as deep as wide, interior often with band of hairs;
sepals 5, spreading to strongly reflexed, usually lanceolate, sometimes ovate to triangular;
petals 5, usually white, sometimes pink- to rose-veined or cream, usually narrowly oblanceolate-elliptic to obovate, sometimes linear to round, usually equal to or longer than sepals;
stamens 10, shorter than petals, filaments usually ± erect, ± flattened, forming tube, anther thecae dehiscing introrsely;
torus conic;
carpels 2–200(–220), glabrous, styles subterminal;
ovule 1.
perianth and androecium perigynous;
epicalyx bractlets present, sometimes absent;
hypanthium usually patelliform, cupulate, or campanulate, sometimes turbinate, saucer-shaped, flat-bottomed, or subglobose to ellipsoid or ovoid;
torus flat to conic or turbinate, enlarged (absent or reduced in Alchemilla, Aphanes, and Chamaerhodos);
carpels 1–260, styles basal or lateral to subterminal, distinct;
ovules 1(or 2), basal.
aggregated achenes, (1–)2–200(–220), obliquely ovoid to reniform, 0.8–3 mm, glabrous;
hypanthium persistent;
sepals persistent, erect;
styles tardily deciduous, jointed, usually ± rough-thickened basally, otherwise mostly filiform.
aggregated achenes (achenes in Alchemilla and Aphanes);
torus sometimes fleshy;
styles deciduous or persistent, not elongate.
= 7.
Horkelia
Rosaceae tribe Potentilleae
Species 20 (20 in the flora).
As discussed under 9. Ivesia, recognition of the ivesioid genera including Horkelia results in a paraphyletic Potentilla, which the first author does not find sufficient to dictate generic circumscriptions. On the basis of morphology and biogeography, Horkelia itself is likely nested within Ivesia as the branch that has radiated primarily within the California Floristic Province (see discussions under Ivesia regarding discordance with M. Töpel et al. 2012, http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0050358). Ivesia in the strict sense consists of an exceptionally diverse array of well-defined species; in contrast, Horkelia is more morphologically coherent as a genus but with species less sharply defined. The primary unifying features of the genus result from a flower specifically adapted for bee pollination: a relatively deep, flat-bottomed hypanthium containing abundant nectar, to which access is restricted by the columnar arrangement of ten erect stamens with flattened filaments, at least in early flowering. Anthers open introrsely by adaxial slits so that pollen is deposited on a visitor forcing its way into the staminal column.
Other diagnostic characteristics of Horkelia include a distinctive resinous aroma in most species (except sect. Tridentatae and sect. Hispidulae) and various levels of glandularity. The terminal leaflet is most often lobed and/or confluent with lateral leaflets, in contrast to Drymocallis, which is often confused with Horkelia. Leaves range from planar with distinct leaflets to cylindric with overlapping leaflets, the latter condition often a response to drought stress in species that are normally planar-leaved. Sepals are often strongly reflexed.
Stem lengths given below include inflorescences. Leaflet descriptions are based primarily on mid rachis leaflets of the larger basal leaves present at flowering; leaflets on the smaller outermost leaves formed early in the growing season are often less divided and less hairy. Counts of leaflet marginal segments include both shallow (teeth) and deep (lobes) ultimate divisions. Flowers are often aggregated into a single corymbiform cluster or one to many more globular glomerules, some of which are tightly capitate. Hypanthia interiors are glabrous in most species, except for the hairs surrounding the torus; some taxa are also more or less pilose on the internal hypanthial walls, especially just below the rim. Sepals are described as spreading or reflexed based on their orientation at anthesis. Larger and smaller anthers often are alternating; measurements are primarily of the larger filaments, with width measured at the base. See under 8. Potentilla and 9. Ivesia for additional discussion of special terminology.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Genera 14–22, species ca. 860 (14 genera, 189 species, including 1 hybrid, in the flora area).
The base chromosome number for Potentilleae is mostly x = 7 (8 in Alchemilla and Aphanes; 14 in Comarum).
Variation in the number of genera recognized in Potentilleae is due to differences in generic delimitation between D. Potter et al. (2007) and the authors of Potentilla and segregates here (see 9. Ivesia and 8. Potentilla for discussion). In the former, Duchesnea, Horkelia, Horkeliella, and Ivesia are included within Potentilla. Likewise, Aphanes is included within Alchemilla by Potter et al. while it is kept distinct here.
Potentilla and its segregates and Fragaria are host to Phragmidium rusts, but not the other genera of the tribe.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Pedicels becoming reflexed or recurved, 3–15 mm; inflorescences open; Sierra Nevada foothills and San Bernardino Mountains, California. | sect. Parryae |
1. Pedicels remaining straight, outermost sometimes ± reflexed in congested inflorescences, 1–30(–40) mm; inflorescences open to congested; w United States | → 2 |
2. Basal leaves: leaflet teeth (0–)3(–5), restricted to apex, leaflets 2–5 per side. | sect. Tridentatae |
2. Basal leaves: leaflet teeth or lobes (0–)4–30(–60), not restricted to apex, leaflets (1–)3–16(–20) per side | → 3 |
3. Plants not resinously aromatic, inconspicuously to moderately glandular; basal leaves ± cylindric to weakly planar; leaflets ± overlapping at least distally, divided 1/2–3/4+ to midrib into (0–)2–8(–15) lobes | → 4 |
3. Plants ± resinously aromatic, conspicuously to obscurely (and minutely) glandular; leaves usually ± planar, sometimes nearly cylindric; leaflets separate to ± overlapping especially distally, divided ± 1/6–3/4+ to midrib into (3–)5–30(–60) teeth or lobes | → 5 |
4. Plants forming dense mats; stems 0.3–2.5 dm; basal leaves: stipules entire; 2000–3400 m; White Mountains, s Sierra Nevada, and Siskiyou Mountains, California, w Nevada, sw Oregon. | sect. Hispidulae |
4. Plants forming rosettes or tufts, sometimes loose mats; stems 0.5–5 dm; basal leaves: stipules entire, forked, or pinnately divided into linear or filiform lobes; 60–2500 m; nw California, sw Oregon. | sect. Tridentatae |
5. Epicalyx bractlets narrowly elliptic-lanceolate to broadly ovate, 0.5–3 mm wide; pedicels 1–30(–40) mm; flowers arranged individually, in usually non-capitate glomerules, and/or in corymbiform clusters; Sierra Nevada foothills and w California. | sect. Horkelia |
5. Epicalyx bractlets linear, 0.2–0.3(–0.5) mm wide; pedicels 1–3(–10) mm; flowers usually arranged in ± capitate glomerules, rarely individually (in H. fusca var. filicoides); Sierra Nevada, California, to Washington and Wyoming. | sect. Capitatae |
1. Shrubs; leaf lobe margins entire; achenes hirsute. | Dasiphora |
1. Herbs, perennial, sometimes annual or biennial, or subshrubs; leaf lobe margins or apices ± toothed, sometimes entire; achenes glabrous (sometimes ± hairy) | → 2 |
2. Petals 0, sepals 4; achenes 1, enclosed in dry, urceolate or subglobose to ellipsoid or ovoid hypanthia | → 3 |
2. Petals and sepals usually 5; achenes 1–260, usually aggregated (sometimes on elongating tori), usually in (± open) patelliform, cupulate, campanulate, or turbinate hypanthia (not enclosed in dry hypanthium) | → 4 |
3. Herbs perennial; leaves basal, blades reniform to orbiculate, palmately lobed, sometimes palmately compound; stamens 4. | Alchemilla |
3. Herbs annual; leaves cauline, blades cuneate, deeply divided into segments, each lobed; stamen 1(or 2). | Aphanes |
4. Leaves all or mostly basal or proximal (if cauline, deeply pinnatifid), ternate or 2–4-ternate (sometimes simple and coarsely toothed apically in Sibbaldia) | → 5 |
4. Leaves basal or cauline, the latter usually reduced distally, odd-pinnate to palmate, rarely ternate or ± bipinnate | → 9 |
5. Tori becoming red and fleshy in fruit; leaf margins serrate to crenate | → 6 |
5. Tori hemispheric (not enlarged or fleshy) in fruit or absent; leaf margins entire or (2–)3(–5)-toothed apically | → 7 |
6. Leaves ± doubly serrate or crenate; stolons leafy; inflorescences: flowers solitary, axillary at stolon nodes; petals yellow. | Duchesnea |
6. Leaves serrate to crenate; stolons not leafy; inflorescences 1–10-flowered, cymes, axillary from leaf rosettes; petals usually white. | Fragaria |
7. Leaves pinnately compound or simple and deeply pinnatifid, margins entire, stipules absent. | Chamaerhodos |
7. Leaves ternate, margins toothed apically, stipules persistent | → 8 |
8. Petals ± yellow; stamens 5. | Sibbaldia |
8. Petals usually white; stamens 20(–30). | Sibbaldiopsis |
9. Petals deep red to purple, rarely pink, shorter than sepals; tori enlarged and spongy at maturity; horizontal stems sometimes floating, wetland habitats. | Comarum |
9. Petals yellow to white, rarely pink or red (then equal to or longer than sepals); tori not enlarged and spongy at maturity; stems erect to decumbent, not horizontal or floating even if in wetlands | → 10 |
10. Anthers dehiscing by continuous marginal slit (with a single theca); styles sub-basal. | Drymocallis |
10. Anthers dehiscing longitudinally; styles subterminal to lateral | → 11 |
11. Hypanthium patelliform to campanulate or cupulate to turbinate (not flat-bottomed); filaments not forming tube; petals white to yellow, sometimes reddish or pink tinged | → 12 |
11. Hypanthium ± cupulate or bluntly campanulate and flat-bottomed; filaments forming tube; petals usually white, sometimes pink-tinged, rose-veined, or cream | → 13 |
12. Plants not aromatic; leaves ± cordate or reniform to narrowly elliptic in outline, leaflets 3–15(–41); petals oblanceolate or obovate to obcordate to nearly round, rarely elliptic; carpels 3–260. | Potentilla |
12. Plants often aromatic; leaves planar to cylindric, leaflets (3–)7–161; petals linear or narrowly oblanceolate to obovate, sometimes obcordate; carpels 1–20(–40). | Ivesia |
13. Stamens 10; leaflets (3–)5–41. | Horkelia |
13. Stamens 20; leaflets 30–70. | Horkeliella |
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