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FNA | Family List | FNA Vol. 20 | Asteraceae | Croptilon

2. Croptilon hookerianum (Torrey & A. Gray) House, Bull. New York State Mus. Nat. Hist. 223: 61. 1921.

Hooker’s scratchdaisy

Isopappus hookerianus Torrey & A. Gray, Fl. N. Amer. 2: 239. 1842; Croptilon divaricatum (Nuttall) Rafinesque var. hookerianum (Torrey & A. Gray) Shinners; Haplopappus validus (Rydberg) Cory subsp. torreyi E. B. Smith

Stems erect, 20–80(–120) cm. Cauline leaf blades lanceolate to linear, reduced distally (becoming bractlike near heads), margins usually serrate apically, rarely entire. Peduncles stipitate-glandular, sometimes hispid as well. Involucres campanulate, (3.5–)5–8(–10) mm diam. Ray florets (10–)13–21(–29); corolla laminae 6–12 mm. Disc florets (20–)33–70(–108). 2n = 10, 12, 14.

Varieties 3 (3 in the flora): sc United States

Morphologic differences among the three varieties are slight and they form a closely coherent group within the genus; corresponding differences in geography, habitat, and chromosome number provide a rationale for maintaining the taxonomic and nomenclatural distinctions. B. L. Turner et al. (2003, vol. 1) treated var. hookerianum as including var. graniticum. B chromosomes sometimes are present and appear to increase the number by a pair (E. B. Smith 1966).

1 Peduncles long-stipitate-glandular (longest hairs 0.4–0.5 mm, including gland), often slightly hispid proximal to heads; ray laminae 1–2.5 mm wide   2a Croptilon hookerianum var. validum
+ Peduncles short-stipitate-glandular (longest hairs 0.2–0.3 mm, including gland), never hispid; ray laminae (1.2–)2–3(–4) mm wide   (2)
2 (1) Peduncles densely stipitate-glandular; ray laminae 1.2–2.2 mm wide; sandy habitats   2b Croptilon hookerianum var. hookerianum
+ Peduncles sparsely stipitate-glandular; ray laminae (1.5–)2–3(–4) mm wide; granitic habitats   2c Croptilon hookerianum var. graniticum


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