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Perennial, generally ± glandular, generally resinous-smelling; caudex generally branched.
Stem: generally ascending to erect.
Leaf: generally basal, odd-1-pinnately compound, generally ± flat; cauline alternate, reduced upward; leaflets 2–15 per side, uppermost lateral generally ± fused with terminal.
Inflorescence: cyme; pedicels generally straight, bractlets 0.
Flower: hypanthium cup-like, ± flat-bottomed, width ± 2 × length, bractlets 5, generally 2/3 sepals; sepals often reflexed; petals generally ± = sepal, blunt, white; stamens 10, filaments ± flat, often forming a tube; pistils 2–many, ovary superior, style attached below fruit tip, ± thicker at base.
Fruit: achene.
20 species: w North America. (J. Horkel, German plant physiologist, 1769–1846) [Ertter & Reveal 2007 Novon 17:315–325] Many attractive to bees; data apply to basal leaves, pressed hypanthia.

Key to Horkelia

1. Fls generally in head-like clusters; plant generally rosetted or tufted; NW, CaR, SN, MP, n SNE — hypanthium bractlets < 0.5 mm wide; hypanthium generally 2–5 mm wide; lower pedicel often reflexed in fruit; > 300 m

2. Lflets 2–5 per side, entire to ± 3-toothed; petal linear to obovate; fruit 1.5–2 mm; 300–2500 m

3. St densely glandular above, ascending to erect; petal generally 2.5–4 mm, generally widely obovate — nw KR ..... H. congesta var. nemorosa

3' St ± glabrous to sparsely glandular above, often decumbent; petal 1.5–4 mm, linear to widely oblanceolate ..... H. tridentata

4. Petal ± widely oblanceolate, often < sepal; hypanthium 2.5–5 mm wide, inner wall hairy (except in NCoRH); KR, NCoR, n SNH ..... var. flavescens

4' Petal generally narrow-oblanceolate, generally >= sepal; hypanthium generally 2–3.5 mm wide, inner wall generally glabrous; CaR, SN, MP ..... var. tridentata

2' Lflets 3–15 per side, > 3-toothed; petal ± wedge-shaped; fruit 1–1.8 mm; > 950 m ..... H. fusca

5. Lflets generally divided ± 3/4 to base, generally 8–15 per side, ± crowded; filament generally < 0.5 mm, generally wider than long — s CaRH ..... var. tenella (2)

5' Lflets generally toothed <= 1/2 to base, generally 4–8 per side, ± separated; filament often > 0.5 mm, generally longer than wide

6. Petal 4–6 mm; leaflets generally 10–20 mm, toothed < 1/4 to base, generally ± obovate; anther ± 0.6 mm; style 1–1.5 mm; fruit ± 1.8 mm; Wrn ..... var. pseudocapitata

6' Petal 2–4 mm; leaflets generally 5–15 mm, toothed 1/4–1/2 to base, ± round to wedge-shaped; anther ± 0.4 mm; style ± 1 mm; fruit 1–1.2 mm; n CA (except Wrn), SNH

7. Lflets ± gray-hairy, narrow-wedge-shaped; CaR, MP ..... var. brownii

7' Lflets green, wedge-shaped to round; e KR, SNH, n SNE ..... var. parviflora

1' Fls generally either in ± flat-topped clusters or inflorescence open; plant often matted; CA-FP, W&I

8. Pedicel ± recurved in fruit; inflorescence open, often ± 1-sided

9. Petal 4–7 mm; leaflets toothed 1/4 to midrib; pistils generally 20–50; n&c SNF (especially Ione Formation) ..... H. parryi

9' Petal 2–3 mm; leaflets lobed 1/2 to 3/4 to base; pistils < 5; SnBr ..... H. wilderae

8' Pedicel erect in fruit; inflorescence open or dense, not 1-sided

10. Filament generally < 0.5 mm, generally wider than long; style ± 1 mm — petal ± wedge-shaped; s CaRH ..... H. fusca var. tenella (2)

10' Filament >= 0.5 mm, generally longer than wide; style 1–4 mm

11. Plant generally rosetted from simple or few-branched caudex; resinous odor weak; leaflets generally < 10-lobed; fruit >= 2 mm; often ± serpentine clay

12. Lflets 5–10 per side, 5–25 mm, lobed > 3/4 to base; stem base hairs 2–3 mm; inflorescence open to dense; hypanthium 3.5–5 mm wide; petal ± obovate, cream; pistils 5–15; style 2.5–4 mm ..... H. daucifolia

13. Lflets ± gray, lobes 2–5, 1–3 mm wide; petal 2–4 mm wide; pedicels nonglandular ..... var. daucifolia

13' Lflets green, lobes 5–15, < 1 mm wide; petal 4–8 mm wide; pedicels glandular ..... var. indicta

12' Lflets ± 15 per side, 2–10 mm, generally lobed ± 1/2 to base; stem base hairs ± 1 mm; inflorescence open; hypanthium 2–3 mm wide; petal obcordate, often pink-tinged; pistils 2–6; style ± 1.5–2 mm

14. Stipules of basal leaves pinnately divided; leaves ± green, 5–15 cm ..... H. howellii

14' Stipules of basal leaves entire or forked; leaves silvery, 3–10 cm ..... H. sericata

11' Plant generally tufted to matted from a few- to many-branched caudex; resinous odor strong; leaflets often > 10-toothed or -lobed; fruit often < 2 mm; generally non-serpentine

15. Lflets pinnately veined, oblong to obovate, ± evenly > 10-toothed — hypanthium width 4–8 mm, > 2 × length, bractlets ± 2–3 mm wide; CW, SW

16. Lflets 1–3 per side, < distinct terminal leaflet, teeth generally double, generally > 20; petal ± round, ± 5 mm wide; 400–1300 m; PR ..... H. truncata

16' Lflets 5–12 per side, ± = generally indistinct terminal leaflet, teeth generally single, ± 10–15; petal obovate or narrower, 1.5–4 mm wide; < 870 m; CCo, SCoRO, SCo ..... H. cuneata

17. Hairs ± all glandular; inflorescence open; hypanthium inner rim ± glabrous; filament base generally 0.5–2 mm wide ..... var. puberula

17' Hairs mostly glandless; inflorescence open to dense; hypanthium inner rim generally hairy; filament base 0.5–1 mm wide

18. Infl generally ± open; hairs ± spreading, ± dense; glands ± obvious ..... var. cuneata

18' Infl dense to ± open; hairs ascending to appressed, dense; glands hidden, if any ..... var. sericea

15' Lflets ± palmately veined at base, wedge-shaped or ± round-ovate, ± unevenly few- to many-toothed or -lobed

19. Hypanthium width 4–10 mm, 1–2 × length, bractlets ovate, generally ± 2 mm wide, ± = sepal; leaflets round to ovate, 5–60 mm, generally ± separated, generally > 20-toothed or -lobed; stem ± leafy; fruit ± 1 mm ..... H. californica

20. Lflets 3–5 per side, generally unlobed, 15–60 mm, elliptic to ovate — hypanthium inner wall glabrous; sepal not red-mottled; style 2–3 mm; CW ..... var. frondosa

20' Lflets 4–9 per side, ± lobed, 5–40 mm, ovate to round

21. Lflets generally few-lobed ± 1/2 to base, 10–40 mm; sepal red-mottled inside; hypanthium bractlets generally toothed; hypanthium inner wall ± hairy; filament generally 1.5–3 mm; style generally 3–4 mm; NCo, CCo ..... var. californica

21' Lflets lobed 1/2–3/4 to base, 5–25 mm; sepal not red-mottled; hypanthium bractlets generally entire; hypanthium inner wall glabrous; filament generally 0.5–1.5 mm; style generally 2–3 mm; NCoR, c&s SN, SnFrB, SnBr ..... var. elata

19' Hypanthium width generally < 6 mm, generally 2+ × length, bractlets lanceolate to ovate, <= 2 mm wide, < sepal; leaflets round to wedge-shaped, generally < 15 mm, often crowded, < 20-toothed or -lobed; stem leaves few, ± reduced; fruit > 1 mm

22. St < 25 cm; hypanthium bractlets generally < 0.5 mm wide; leaves 2–10 cm; fruit 1.5–2.5 mm; > 2000 m; KR, s SNH, W&I

23. Hypanthium densely hairy on inner rim; sepal 3.5–6 mm, 2+ × hypanthium length; longer hairs ± 1 mm, soft — ne KR ..... H. hendersonii

23' Hypanthium ± hairy on inner wall; sepal generally 2–4 mm, < 2 × hypanthium length; longer hairs ± 0.5 mm, stiff

24. Lflets generally 10–14 per side, generally 2.5–4 mm; pistils 10–20; W&I ..... H. hispidula

24' Lflets generally 4–6 per side, generally 3.5–8 mm; pistils 5–12; s SNH ..... H. tularensis

22' St 10–70 cm; hypanthium bractlets generally >= 0.5 mm wide; leaves 3–20 cm; fruit 1.5–2 mm; < 2800 m; NCo, NCoR, CW, SW

25. St decumbent to ascending, generally 10–30 cm; plant matted, odor strong; inflorescence ± dense; leaves generally 4–10 cm; leaflets generally 5–10 per side, ± crowded — hairs dense; NCo, CCo ..... H. marinensis

25' St ascending to erect, 10–70 cm; plant tufted or matted, odor strong or not; inflorescence generally ± open; leaves generally 3–20 cm; leaflets 6–16 per side, separated or crowded

26. Hypanthium bractlets 1–2 mm wide, lanceolate to ovate; anther ± 1 mm — hypanthium generally 3–6 mm wide; stem hairs spreading; SCoRO ..... H. yadonii

26' Hypanthium bractlets generally 0.5–1 mm wide, linear or elliptic to lanceolate; anther 0.5–1 mm

27. St and petiole hairs generally spreading; plant often green

28. Lflets toothed ± 1/3 to base; hypanthium inner wall glabrous; PR ..... H. clevelandii var. clevelandii

28' Lflets divided > 1/2 to base, lobes linear to oblanceolate; hypanthium inner wall ± hairy; NCo, NCoRO, SnFrB ..... H. tenuiloba

27' St and petiole hairs generally ascending to appressed; plant generally ± gray — hypanthium inner wall ± hairy

29. Lf 3–8 cm; pistils generally 10–20; style 1–2 mm; NCoRI ..... H. bolanderi

29' Lf 4–20 cm; pistils generally 20–50; style generally 2–3 mm; TR ..... H. rydbergii

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Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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