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Santa Rosa, Santa Rosa horkelia, Sonoma horkelia, thin-lobed, thin-lobed horkelia

Howell's horkelia, Klamath horkelia

Habit Plants loosely matted, green. Plants tufted to openly matted, ± green.
Stems

ascending to erect, 1–4 dm, hairs ± spreading.

ascending to erect, (0.9–)1.5–5 dm, hairs 1 mm proximally, glands absent or sparse distally.

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.

± cylindric to weakly planar, 5–15 × 0.5–1.8(–2.5) cm, usually villous to pilose at least marginally, often glabrescent;

stipules deeply 2-lobed or pinnately divided into 3–5 linear to filiform lobes that often form a tangled mass;

leaflets 10–15 per side, ± overlapping, elliptic to flabellate, (3–)4–10(–15) × 2–8 mm, 1/2 to as wide as long, divided 1/2–3/4 to midrib into (0–)2–4 elliptic to linear lobes 1–2 mm wide, these not restricted to apex.

Cauline leaves

2–5.

(2 or)3–5;

stipules 5–12(–15) mm, entire to deeply 2–4-lobed or -toothed (usually on 1 side).

Inflorescences

open to congested, flowers arranged individually and in glomerules, these sometimes subcapitate.

open, flowers arranged individually and/or in non-capitate glomerules.

Pedicels

1–6 mm.

1–6(–12) mm.

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.

10 mm diam.;

epicalyx bractlets linear-lanceolate, 1–3 × 0.5 mm, ± 2/3 length of sepals;

hypanthium 1.1–1.5 × 2–3 mm, ± 1/2 to as deep as wide, interior glabrous;

sepals spreading to reflexed, abaxially green to reddish or purplish, 2.5–4.5 mm;

petals white to pink or red-veined, narrowly obcordate, 3–5 × 2–3 mm, apex truncate or emarginate;

filaments 0.5–1.7 × 0.2–0.5 mm, anthers 0.4–0.6 mm;

carpels 2–6;

styles 1.5–2 mm.

Achenes

light brown, 1.5 mm, smooth or slightly rugose.

brown, 2–2.7 mm, smooth.

2n

= 28.

Horkelia tenuiloba

Horkelia howellii

Phenology Flowering summer. Flowering summer.
Habitat Sandy soil, openings, in chaparral, oak woodlands Chaparral, oak-conifer woodlands, mainly on serpentine soil
Elevation 50–500 m (200–1600 ft) 60–1200 m (200–3900 ft)
Distribution
from FNA
CA
[WildflowerSearch map]
[BONAP county map]
from FNA
CA; OR
[WildflowerSearch map]
[BONAP county map]
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.)

Of conservation concern.

As noted above, Horkelia howellii comprises the bulk of what D. D. Keck (1938) and subsequent floras included in H. sericata, and the range of the latter is fully encompassed within that of the former. As here circumscribed, H. howellii occurs in northwestern California and southwestern Oregon. The handful of collections from Humboldt and Trinity counties, California, including the type of Potentilla laxiflora Drew, have leaves approaching H. daucifolia but the inflorescence of H. howellii; exact petal color is uncertain.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 9, p. 252. FNA vol. 9, p. 265.
Parent taxa Rosaceae > subfam. Rosoideae > tribe Potentilleae > Horkelia > sect. Horkelia Rosaceae > subfam. Rosoideae > tribe Potentilleae > Horkelia > sect. Tridentatae
Sibling taxa
H. bolanderi, H. californica, H. clevelandii, H. congesta, H. cuneata, H. daucifolia, H. fusca, H. hendersonii, H. hispidula, H. howellii, H. marinensis, H. parryi, H. rydbergii, H. sericata, H. tridentata, H. truncata, H. tularensis, H. wilderae, H. yadonii
H. bolanderi, H. californica, H. clevelandii, H. congesta, H. cuneata, H. daucifolia, H. fusca, H. hendersonii, H. hispidula, H. marinensis, H. parryi, H. rydbergii, H. sericata, H. tenuiloba, H. tridentata, H. truncata, H. tularensis, H. wilderae, H. yadonii
Synonyms H. fusca var. tenuiloba, Potentilla micheneri, P. stenoloba Potentilla howellii
Name authority (Torrey) A. Gray: Proc. Amer. Acad. Arts 6: 529. (1865) (Greene) Rydberg: Bull. Torrey Bot. Club 25: 55. (1898)
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