keys to the vascular plants of east texas - Botanical Research ...

624 CYPERACEAE/RHYNCHOSPORA
17. Surface of achenes horizontally ridged, rugose (= wrinkled), pitted, or
honeycombed-reticulate (use magnification).
22. Perianth bristles absent (can be absent in R. perplexa); achenes 0.9
mm or less long; tubercle minute, to 0.15 mm long.
23. Surface of achenes horizontally ridged (use hand lens or dissecting
scope), not glassy in appearance ______________________ R. pusilla
23. Surface of achenes faintly reticulate (using dissecting scope),
but not horizontally ridged, somewhat glassy in appearance
____________________________________________________ R. divergens
22. Perianth bristles usually present; achenes 1–2.2 mm long; tubercle
larger, > 0.15 mm long.
24. Culms and leaves filiform-wiry, almost thread-like, 1 mm or less wide.
25. Perianth bristles shorter than achenes; tubercle deltoid to
deltoid-conical, 0.3–0.6 mm long; spikelets 3–4(–4.5) mm
long ______________________________________________ R. rariflora
25. Perianth bristles longer than achenes; tubercle taller and
narrower, deltoid-subulate, 0.8–1.5 mm long; spikelets 4–5
mm long _______________________________________ R. stenophylla
24. Culms and leaves stouter, not filiform-wiry, usually > 1 mm wide.
26. Faces of the achenes flat or concave.
27. Spikelets 5–7(–9) mm long; achenes 2 times as long as
wide or longer, 2–2.5 mm long; tubercle 0.8–1.2 mm
long __________________________________________ R. inexpansa
27. Spikelets 2–3.5 mm long; achenes < 2 times as long as
wide, 1–1.3 mm long; tubercle 0.2–0.5(–0.7) mm long.
28. Perianth bristles 6, surpassing the tubercle, often
widely spreading; leaf blades 3–6 mm wide _________ R. elliottii
28. Perianth bristles 0–3(–6), absent or rudimentary, if
present, < three-fourths as long as the achenes, not
widely spreading; leaf blades 1.5–2.5 mm wide _____ R. perplexa
26. Faces of the achenes convex or swollen, sometimes with a central bulge.
29. Inflorescence branches spreading nearly at right angles to the main inflorescence axis, the
inflorescence appearing very open, each spikelet or small cluster of spikelets on a slender
stalk; achenes yellowish to greenish yellow, tan, or pale brown _________________________ R. miliacea
29. Inflorescence branches ascending, the inflorescence not as above; achenes brown to black.
30. Spikelets 4–6(–7.5) mm long; achenes 2–2.5 mm long; plants of droughty sandhills,
typically with longleaf pines ____________________________________________________ R. grayi
30. Spikelets usually 2–4 mm long (to 5 mm long in R. caduca); achenes usually 1–1.8 mm
long; plants of wet to seasonally moist habitats.
31. Perianth bristles shorter than the achenes.
32. Surface of achenes with horizontal rows of cells nearly circular in outline, brown
to dark brown or almost black; summit of achenes often abruptly narrowed,
with a distinct, smooth, collar-like ring or ridge fitted against the tubercle _______ R. harveyi
32. Surface of achenes with horizontal rows of vertically oriented cells rectangular
in outline, light brown to brown; summit of achenes usually gradually narrowed
to tubercle base, usually lacking a collar-like ring or ridge.
33. Achenes 1–1.2 mm long, 0.8–1 mm wide; species possibly present in East
TX __________________________________________________________ R. microcarpa
33. Achenes 1.2–1.8 mm long, 1–1.5 mm wide; species widespread and abundant
in East TX.