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Key to families | Table of families and genera

Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.

 

TETRADYMIA COTTONTHORN, HORSEBRUSH
Shrub. Stem: ± tomentose. Leaf: alternate and generally clustered in axils, linear to (ob)lanceolate, sometimes persisting as stiff spines, glabrous to tomentose. Inflorescence: heads discoid, axillary or in ± rounded or flat-topped, terminal clusters; involucre cylindric to hemispheric; phyllaries 4–6 in 1–2 ± equal series, often keeled; receptacle flat, epaleate. Disk flower: 4–9; corolla cream to yellow, lobes long, spreading or recurved; anther base ± sagittate, tip obtuse or acute; style branches papillate to short-bristly, tips truncate to conic. Fruit: obconic or fusiform, often 5-angled; pappus 0 or of generally many bristles or slender scales.
10 species: western North America. (Greek: 4 together, from 4-flowered heads of some species) Esp flower buds TOXIC to sheep (toxicity poorly understood). [Strother 2006 FNANM 20:629–632]
Unabridged references: [Strother 1974 Brittonia 26:177–202]

Key to Tetradymia

1. Stem unarmed (leaves not forming spines)

2. Flowers (5)6–9 per head; pappus 0 (but fruit covered with long, pappus-like hairs); axillary leaf clusters generally 0 ..... T. comosa (2)

2' Flowers 4(5) per head; pappus present; axillary leaf clusters generally present

3. Main leaves tomentose or silvery; clustered leaves ± (ob)lanceolate ..... T. canescens

3' Main leaves glabrous or sparsely tomentose; clustered leaves thread-like to linear-oblanceolate

4. Main leaves narrowly awl-shaped, stiffly ascending or appressed, generally 5–10 mm; clustered leaves generally 3–10 mm, glabrous; fruit generally 3–4 mm, short-stiff-hairy; pappus of ± 100 bristles ..... T. glabrata

4' Main leaves ± thread-like, soft, 10–40 mm; clustered leaves generally 10–20 mm, loosely tomentose; fruit 5–6 mm, long-soft-hairy; pappus of ± 20 stiff bristles or slender scales (± hidden by fruit hairs) ..... T. tetrameres

1' Stem armed with spines derived from main leaves

5. Fruit glabrous, 2.5–3.5 mm ..... T. argyraea

5' Fruit ± long-soft-hairy, 4–8 mm

6. Main leaves narrowly (ob)lanceolate, finally deciduous, base not hardened; pappus 0 ..... T. comosa (2)

6' Main leaves tapered to tip, persistent as stout spines, base expanded, hardened; pappus present

7. Clustered leaves tomentose or silvery-hairy; fruit ± short-hairy; pappus of many fine bristles 9–12 mm ..... T. stenolepis

7' Clustered leaves ± glabrous; fruit densely long-hairy; pappus of ± 25 slender scales 6–9 mm

8. Spines sharply recurved, 5–25 mm, tomentose; involucre generally 8–12 mm, ± bell-shaped; fruit generally 6–8 mm ..... T. spinosa

8' Spines straight, (1)2–5 cm, becoming glabrous; involucre generally 7–9 mm, obconic; fruit generally 4–5 mm ..... T. axillaris

9. Involucre and peduncle glabrous; fruit hairs generally 6–8 mm ..... var. axillaris

9' Involucre and peduncle tomentose; fruit hairs generally 9–11 mm ..... var. longispina

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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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