Many botanists in the southeastern United States consider Sorghastrum apalachicolense to be a good species. The arguments can be found in D.W. Hall, Sorghastrum (Poaeae) in Florida [Sida 9:302-308 (1982)] and B.A. Sorrie and S.W. Leonard, Noteworthy records from Mississippi [Sida 18:889-908 (1999)]. The following key may be used to identify the four species that grow in the United States if S. apalachicolense is recognized.
1 |
Awns
10-22 (30) mm long, once geniculate; plants rhizomatous ..... S. nutans |
Awns 21-40 mm long, twice-geniculate;
plants not rhizomatous (2) |
|
Pedicels sharply
curved to recurved; panicles secund; sessile spikelets 0.8-1.2
mm wide ..... S. secundum |
|
Pedicels flexuous; panicles not
secund; sessile spikelets 1.1-1.8 mm wide (3) |
|
Panicles conspicuously
arching; spikelets 1.4-1.4 mm wide .... S. elliottii |
|
Panicles straight; spikelets 1.3-1.8
mm wide ..... S. apalachicolense |
The following description is based on Hall (1982) and Sorrie and Leonard (1999).
Sorghastrum apalachicolense Hall
Open Indiangrass
Plants perennial; cespitose, not rhizomatous. Culms erect. Sheaths
pubescent; blades to 43 cm long and 7.3 mm wide, flat or slightly folded,
scabrous abaxially, glabrous adaxially. Panicles 23.5-32.5 cm long,
4.5-10.5 cm wide (including the awns), straight, diffuse; rachises 1.3-1.8 mm
thick, 1-2 above the lowest node; nodes with a ring of bristles; longest
branches 7.5-11.1 cm long, ascending before and after anthesis, strongly
divergent during anthesis. Spikelets 5.7-7.2 mm long, 1.3-1.8 mm wide,
pubescent, dark brown to golden brown at maturity. Awns 21-38 mm,
twice-geniculate, twisted. Pedicels 4-5.4 mm, flexuous.
Sorghastrum applachicolense grows on elevated sites in wet savannahs
and longleaf-wiregrass ridges. It flowers from July to August, about a month
earlier than S. elliottii and two weeks earlier than S. secundum,
although its flowering time does overlap somewhat with S. secundum. Plants
collected before or after anthesis are easily confused with S. secundum
because their branches are ascending at those times; it is only during anthesis
than the branches are spreading. It differs from S. secundum in having a
distinct ring of bristlelike hairs around the rachis nodes; these bristles are
strongly reduced or absent in S. secundum.
The distribution map for Sorghastrum secundum includes S.
apalachicolense. Sorrie and Leonard reported that they knew of no record
of S.
secundum, as they interpret that species, from west of the Mobile-Tensaw
Delta, Alabama.
Hatch and Dávila consider S. apalachicolense to be no more than a
local variant of S. elliottii. It is their treatment that is
followed in Flora of North America, volume 25. Further investigation
of the status of the non-rhizomatous members of Sorghastrum growing
in the United States and Mexico, possibly employing transplanting, hybridization,
isozymes, or nucleic acids, would be interesting.