Pterocaulon pycnostachyum
coastal blackroot, dense-spike blackroot, fox-tail blackroot
blades lanceolate 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.
campanulate, 4–5 mm.
23–44.
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).
1–1.3 mm.
staminate florets 6–10(–15).
= 20.
Pterocaulon pycnostachyum
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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