Horkelia tenuiloba |
Rosaceae tribe Potentilleae |
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Santa Rosa, Santa Rosa horkelia, Sonoma horkelia, thin-lobed, thin-lobed horkelia |
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Habit | Plants loosely matted, green. | Herbs, perennial, rarely annual or biennial, shrubs, or subshrubs; unarmed. | ||||||||||||||||||||||||||||||||||||||||||||||||||||
Stems | ascending to erect, 1–4 dm, hairs ± spreading. |
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Leaves | alternate, rarely opposite, pinnately (palmately) compound (simple in Alchemilla, Aphanes, and Chamaerhodos); stipules persistent (absent in Chamaerhodos), adnate to petiole; venation pinnate or palmate. |
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Basal leaves | weakly planar to ± cylindric, 5–15(–20) × 0.5–1.5 cm; stipules entire; leaflets 8–16(–20) per side, ± overlapping especially distally, cuneate to flabellate, 3–10 × 2–10 mm, 1/2 to nearly as wide as long, divided 1/2–3/4+ to midrib into 3–8 linear to narrowly oblanceolate or narrowly elliptic lobes, sparsely villous at least marginally, often with a tuft of hairs apically. |
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Cauline leaves | 2–5. |
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Inflorescences | open to congested, flowers arranged individually and in glomerules, these sometimes subcapitate. |
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Pedicels | 1–6 mm. |
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Flowers | 10 mm diam.; epicalyx bractlets narrowly to broadly lanceolate, 1–3 × 0.5–1 mm, slightly shorter than sepals, entire; hypanthium 1–1.2 × 2.5–4.5 mm, less than 1/2 as deep as wide, interior pilose; sepals spreading to reflexed, lanceolate, 3–5 mm; petals oblanceolate, 2.5–4.5 × 1.5 mm, apex emarginate; filaments (1–)1.5–2 × 0.5 mm, anthers 0.4–0.6 mm; carpels 10–25; styles 1.8–2.2 mm. |
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. |
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Fruits | aggregated achenes (achenes in Alchemilla and Aphanes); torus sometimes fleshy; styles deciduous or persistent, not elongate. |
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Achenes | light brown, 1.5 mm, smooth or slightly rugose. |
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2n | = 28. |
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Horkelia tenuiloba |
Rosaceae tribe Potentilleae |
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Phenology | Flowering summer. | |||||||||||||||||||||||||||||||||||||||||||||||||||||
Habitat | Sandy soil, openings, in chaparral, oak woodlands | |||||||||||||||||||||||||||||||||||||||||||||||||||||
Elevation | 50–500 m (200–1600 ft) | |||||||||||||||||||||||||||||||||||||||||||||||||||||
Distribution |
CA
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North America; Mexico; Central America; South America; West Indies; Bermuda; Eurasia; Africa; Atlantic Islands; Pacific Islands; Australia |
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Discussion | Of conservation concern. Horkelia tenuiloba occurs on the western edges of the northern Coast Ranges in Marin, Mendocino, and Sonoma counties. Populations from San Luis Obispo formerly included in this species now are part of H. yadonii. A specimen (M. K. C[urran], July 5, 1885, UC) unequivocally of H. tenuiloba purportedly from San Luis Obispo is in all likelihood mislabeled with respect to locality. Horkelia tenuiloba is commonly associated with seral openings in chaparral and woodlands and might be dependent on periodic disturbance by fire. W. L. Jepson (1909–1943, vol. 2) used Potentilla stenoloba (1895) for the species encompassing the types of Horkelia tenuiloba and P. micheneri. The epithet micheneri (1893) has priority at species rank within Potentilla, since P. tenuiloba (Torrey) Greene is a later homonym of P. tenuiloba Jordan. (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.) |
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Key |
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Source | FNA vol. 9, p. 252. | FNA vol. 9, p. 119. | ||||||||||||||||||||||||||||||||||||||||||||||||||||
Parent taxa | Rosaceae > subfam. Rosoideae > tribe Potentilleae > Horkelia > sect. Horkelia | Rosaceae > subfam. Rosoideae | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Synonyms | H. fusca var. tenuiloba, Potentilla micheneri, P. stenoloba | |||||||||||||||||||||||||||||||||||||||||||||||||||||
Name authority | (Torrey) A. Gray: Proc. Amer. Acad. Arts 6: 529. (1865) | Sweet: Brit. Fl. Gard. 2: sub plate 124. (1825) | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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