Croptilon hookerianum

(Torrey & A. Gray) House

Bull. New York State Mus. Nat. Hist. 223: 61. 1921.

Common names: Hooker’s scratchdaisy
Basionym: Isopappus hookerianus Torrey & A. Gray Fl. N. Amer. 2: 239. 1842
Synonyms: Croptilon divaricatum var. hookerianum (Torrey & A. Gray) Shinners Haplopappus validus subsp. torreyi E. B. Smith
Treatment appears in FNA Volume 20. Treatment on page 229.

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).

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).

Selected References



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 Croptilon hookerianum var. validum
1 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 Peduncles densely stipitate-glandular; ray laminae 1.2–2.2 mm wide; sandy habitats Croptilon hookerianum var. hookerianum
2 Peduncles sparsely stipitate-glandular; ray laminae (1.5–)2–3(–4) mm wide; granitic habitats Croptilon hookerianum var. graniticum