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FNA | Family List | FNA Vol. 19, 20 and 21 | Asteraceae | Pterocaulon

1. Pterocaulon pycnostachyum (Michaux) Elliott, Sketch Bot. S. Carolina. 2: 324. 1823.

Fox-tail or coastal blackroot

Conyza pycnostachya Michaux, Fl. Bor.-Amer. 2: 126. 1803; Pterocaulon undulatum C. Mohr

Plants 2–8 dm. Leaf blades lance-olate to obovate-lanceolate, oblong, or elliptic, 3–11 × 1–3(–3.5) cm, lengths mostly 2–7 times widths, margins usually dentate or denticulate, slightly repand, sometimes nearly entire. Heads in dense, usually contin­uous, rarely interrupted (then near bases), narrow, ± ovoid arrays (2–)3–8(–10) cm (usually single, sometimes with 1–2 basal branches). Involucres campanulate, 4–5 mm. Pistillate florets 23–44. Functionally staminate florets 6–10(–15). Cypselae 1–1.3 mm. 2n = 20.

Flowering May–Jun. Sandy pinelands, sandy fields, depressions, ditches; 0–20 m; Ala., Fla., Ga., Miss., N.C., S.C.

Differences between Pterocaulon pycnostachyum and P. alopecuroides (Lamarck) de Candolle, which is widespread in the West Indies and South America, are these: plants 50–70 cm high in P. pycnostachyum (versus 70–150 cm in P. alopecuroides), arrays of heads 4–8 cm (versus 3–17 cm) long, involucres 3.5–4 mm (versus 4.5–5 mm) high, and 6–15 (versus 1–3) functionally staminate florets (A. L. Cabrera and A. M. Ragonese 1978). In P. alopecuroides, the arrays of heads are almost always interrupted proximally, commonly producing sessile to subsessile branches. A count of functionally staminate florets provides a clear determinant for plants that might appear ambiguous in other features.


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