Dichanthelium

This large and difficult genus was included in Panicum in Michigan Flora. See the review of Dichanthelium in Michigan by S. N. Stephenson (1984) for detailed information and an alternative key. While fully acknowledging the difficulty of the genus, we nevertheless recognize a number of entities at species rank that were listed as subspecies in Flora North America. But clearly, the genus is still in need of much careful collecting and more systematic work in Michigan.

The species flower twice, with terminal (vernal) panicles in the early summer and lateral (autumnal) panicles in late summer or fall. The key is designed for use with early panicles. The autumnal form may appear quite different, and autumnal foliage and spikelets are unsatisfactory for determination.

1. Spikelets glabrous.

2. Spikelets all or mostly 3 mm or more in length, strongly nerved.

D. depauperatum (in part)

2. Spikelets less than 3 mm long, strongly nerved or not.

3. Spikelets ca. 2 (1.8–2.3) mm long at maturity; nodes glabrous, minutely pubescent or rarely with spreading hairs.

D. dichotomum (in part)

3. Spikelets ca. 1.5–1.7 mm long; nodes with prominent retrorse beard.

D. microcarpon

1. Spikelets at least sparsely pubescent toward their margins.

4. Widest leaf blades over 15 mm broad.

5. Sheaths of all leaves glabrous or with soft pubescence, the hairs not papillose-based (or rarely marginal cilia weakly so).

6. Spikelets 1.4–1.7 mm long.

D. polyanthes (in part)

6. Spikelets 3–4 mm long.

D. latifolium

5. Sheaths of at least lower and middle leaves (especially on leafy branches) with papillose-based hairs (or papillae obvious on backs of sheaths even if hairs are gone).

7. Spikelets 3.5–4 mm long; first glume half as long as spikelet; panicle with fewer than 40 (–50) spikelets, well exserted.

D. xanthophysum (in part)

7. Spikelets 2.9–3.4 (–3.6) mm long; first glume usually slightly less than half as long as spikelet; panicle (at least exserted terminal one) with more than 50 spikelets, often (especially later and axillary ones) with base included in sheath.

D. clandestinum

4. Widest leaf blades less than 15 mm broad.

8. Longest leaf blades at least 20 times as long as wide (not over 5 or very rarely 6 mm wide); leaves all appearing crowded toward base of plant (internodes few and short), erect, and all elongate, the plants not forming rosettes of short stubby leaves.

9. Second glume and sterile lemma distinctly prolonged (usually 0.5–1 mm) beyond the fertile lemma, forming an acute boat-shaped tip or beak to the spikelet; largest spikelets (3–) 3.2–4.1 (–4.5) mm long.

D. depauperatum (in part)

9. Second glume and sterile lemma barely if at all prolonged beyond mature fertile lemma, the mature spikelet ± blunt (if shortly beaked, then only ca. 2.5 mm long); spikelets (2–) 2.2–3.1 (–3.3) mm long.

10. Spikelets (2–) 2.2–2.6 mm long, 1.2–1.4 mm wide; panicle at maturity ± open, the longest pedicels 8–18 mm long.

D. linearifolium

10. Spikelets 2.8–3.1 (–3.3) mm long, 1.6–1.8 mm wide at maturity; panicle narrow (at most 1–1.5 cm wide), the longest pedicels seldom over 1 mm long.

D. perlongum

8. Longest leaf blades less than 15 (–20) times as long as wide (width various); leaves ± distributed on the culm, spreading or ascending (not all crowded basally and erect), the plants usually forming basal rosettes of short stubby leaves.

11. Largest spikelets (3–) 3.1–3.8 (–4) mm long.

12. First glume very broadly ovate, not over 1.5 (–1.7) mm long, its tip distinctly below the middle of the sterile lemma beneath it; ligule of hairs ca. (0.5–) 1–1.5 mm long; spikelets sparsely short-hairy (hairs less than 0.5 mm long).

D. oligosanthes

12. First glume narrowly ovate, 1.6–2.5 mm long, its tip reaching to or beyond the middle of the sterile lemma; ligule very short or vestigial, scarcely 0.5 mm long (longer hairs at sheath margin); spikelets short- or long-hairy.

13. Spikelets with long soft spreading hairs (the longest ca. 1 mm); leaf blades pubescent.

D. leibergii

13. Spikelets minutely hairy; leaf blades glabrous (except for few cilia at base).

D. xanthophysum (in part)

11. Largest spikelets less than 3 mm long.

14. Middle and upper internodes and usually sheaths (except for ciliate margin) glabrous; axis of panicle glabrous or nearly so, without long hairs.

15. Longest hairs of ligules ca. 1.5–3 mm or more; spikelets 1.3–1.8 mm long.

16. Panicle branches ± spreading, the panicle more than half as wide as long; pedicels of lateral spikelets all or nearly all longer than spikelets; middle and upper leaf sheaths of primary stems usually with long marginal cilia.

D. lindheimeri

16. Panicle branches ± strongly ascending, the panicle half or less as wide as long; pedicels of lateral spikelets mostly equaling or shorter than spikelets; middle and upper leaf sheaths of primary stems lacking long marginal cilia.

D. spretum

15. Longest hairs of ligules less than 1 (–1.5) mm long; spikelets 1.4–3 mm long.

17. Spikelets 1.4–1.7 mm long; ligule, at least on upper leaves, vestigial (rarely a short fringe).

18. Longest leaf blades 13–22 cm long; fully expanded panicles mostly 2–3 times as long as wide.

D. polyanthes (in part)

18. Longest leaf blades 5–13 cm long; fully expanded panicles mostly less than twice as long as wide.

D. sphaerocarpon

17. Spikelets ca. 1.8–2.2 mm or more long; ligule a short (usually less than 1 mm) but definite fringe of hairs.

19. Leaf blades mostly 6–9 (–12) mm wide; spikelets usually conspicuously, though finely, pubescent.

D. boreale

19. Leaf blades less than 6 mm wide; spikelets very sparsely puberulent or glabrate.

D. dichotomum (in part)

14. Middle and upper internodes and usually sheaths puberulent to pilose (or both); axis of panicle often with some long hairs.

20. Spikelets (2.1–) 2.3–2.9 mm long (pubescence of leaf sheaths of very short hairs, with or without additional long hairs).

21. Pubescence of leaf sheaths, and usually culms, of short puberulence (best seen on upper sheaths and culms, rarely nearly absent) plus ± sparse to copious long hairs intermixed (best seen on lower sheaths); ligule a definite fringe of hairs usually ca. 0.5–4 mm long.

D. commonsianum

21. Pubescence of leaf sheaths and culms exclusively of sparse to dense fine short hairs (less than 0.5 mm long) except along margin of sheath; ligule absent or very short.

D. commutatum

20. Spikelets not over 2 mm long, mostly a little less (if rarely up to 2.2 mm in D. praecocius, the sheaths with only long spreading hairs).

22. Sheaths of main (vernal) culm with double vestiture (two types of pubescence): short hairs like those on the spikelets (best seen on upper sheaths) and long hairs (best seen on lower sheaths), the two most clearly intermixed on middle sheaths.

23. Spikelets mostly (1.6–) 1.7–1.9 (–2) mm long; leaf blades glabrous to sparsely pilose on upper surface, the largest on culm leaves often more than 4 mm wide or longer than 5 cm.

D. columbianum

23. Spikelets mostly 1.3–1.6 mm long; leaf blades pilose with ± erect hairs on upper surface, the largest blades on culm leaves less than 4 mm wide and up to 5 cm long.

D. meridionale

22. Sheaths of main (vernal) culms with a single type of pubescence: all hairs long (though not necessarily uniform).

24. Middle and upper sheaths with spreading to ascending hairs less than 3 mm long (except sometimes marginal cilia); spikelets (1.4–) 1.5–1.8 (–2) mm long, the first glume very short, usually no longer than broad and ± obtuse, rounded, truncate, or erose.

D. implicatum

24. Middle and upper sheaths pilose with ± horizontally spreading very fine hairs, many of them ca. 3–4 mm long; spikelets ca. 1.8–2 (–2.2) mm long, the first glume a little longer than broad and definitely acute.

D. praecocius