Aristida longespica (Slimspike Three-awn)
|Also known as:
|part shade, sun; dry sandy soil; prairies, meadows, open woods
|August - October
|12 to 15 inches
|Wetland Indicator Status:
|GP: FACU MW: FACU NCNE: FACU
|MN county distribution (click map to enlarge):
|National distribution (click map to enlarge):
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Loose, raceme-like branching cluster 6 to 7½ inches long at the top of the stem, with smaller lateral clusters arising from leaf axils which are often at least partially enclosed in the leaf sheaths. Branches are mostly erect, with 2 to 5 spikelets (flower clusters) per branch. Spikelets are short-stalked, single-flowered, often purplish, the body 6 to 11 mm (¼ to ~3/8 inch) long, narrowly lance-elliptic in outline.
At the base of a spikelet is a pair of bracts (glumes), both similar, thin and papery, hairless, 1-veined, narrowly lance-shaped tapering to a pointed tip or with a short awn (1 mm) extension, the body 2 to 11 mm long, the upper glume about equal or slightly longer than the lower glume and slightly longer than the floret. Florets are surrounded by a pair of bracts (lemma and palea), the lemma thicker than the glumes, 3-veined, the body 4 to 10 mm long, mottled gray or brown, hairless or sparsely rough-hairy, narrowly lance-linear with a 3-branched awn at the tip, the central branch 1 to 27 mm (to 1 inch) long, the lateral branches 0 to 18 mm, all angled at the base and not coiled (awns are all initially straight and twist with age); the palea is obscure and mostly enclosed by the lemma. The thickened base of the floret (callus) is covered in straight, white hairs.
Leaves and stems:
Leaves are basal and alternate on the lower half of the stem, up to 5½ inches long, .5 to 2 mm wide, hairless, lance-linear, flat or the edges rolled in (involute). The sheath is loose, has thin, papery edging and is hairless or with sparse soft hairs near the tip. The ligule (membrane where the leaf joins the sheath) is fringed with short hairs less than 1 mm long. Nodes are smooth. Stems are hairless, few to many branched at or near the base, erect to ascending or spreading from the base and rising at the lower node (geniculate), and forming clumps.
The Aristida genus is a fairly large group of small to medium sized, clump forming grasses that are mostly associated with dry, sandy soils. They are commonly called three-awn grasses due to the three-parted awn at the tip of the lemma. Structurally there is a central and two lateral awns and the relative differences in length and degree of twisting of these awns is a primary diagnostic to their identification; many are readily distinguished on this characteristic alone, but the twisting may not be distinctive until maturity. There are six species found in Minnesota, and while three of the six are state listed as rare, from a field encounter perspective, the other three are relatively uncommon but for a few specific sites. A. longespica was unknown in Minnesota until 1999 when a small fragmented population was discovered in southern Anoka county. Because subsequent surveys failed to locate additional populations and the ongoing intense development pressure of its habitat, it was listed as state Endangered in 2013.
The are two recognized varieities of Aristida longespica: var. longespica, found to our south and east, has smaller spikelets and awns, glumes 2 to 8 mm long, the central awn rarely more than 10 mm long, the lateral awns half or less the size and sometimes absent altogether; var. geniculata, found in Minnesota, has larger spikelets and awns, glumes 4 to 11 mm long, the central awn 12 to 27 mm (to 1 inch) long, and lateral awns half to nearly as long.
A. longespica var. geniculata can be distinguished from the other Minnesota Aristida species by the 3 awns all 1 inch or less long, and all 3 angled or curved out near the base but not coiled. It is most similar to Aristida basiramea and A. dichotoma. The former has a central awn up to 15 mm long that is coiled at the base and lateral awns at least half as long that are loosely coiled or angled at the base. The latter also has a coiled central awn but the lateral awns are much shorter, straight and erect. While the general form of A. longespica also resembles the remaining three other Aristida species in Minnesota, they all have awns usually all about equal in length and 1 to several inches long.
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- Aristida longespica plants
- Aristida longespica plants
- Aristida longespica illustration
- comparison of Aristida basiramea, A. dichotoma and A. longespica spikelets
- comparison of Aristida longespica, A. purpurea and A. tuberculosa spikelets
Photos by Peter M. Dziuk taken in Anoka County.
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