Andropogon gerardii
 
Big Bluestem

Sessile Spikelet - Glume B

Intersection of Highways # 9 and # 247
21-July-2023

The spikelet unit in this species consists of a sessile spikelet, a hairy pedicel with a sterile spikelet at the tip, and a hairy rachis joint, all arising from the same point.  The spikelet units are joined end to end along the rachis joints to form a rame. Note the lemma awn from the sessile spikelet is 8-20 mm long.

The following items are taken from keys in Flora of Saskatchewan, Fascicle 4, Grasses of Saskatchewan by Anna L. Leighton and Vernon L. Harms.  Family Poaceae is first divided into tribes, then the tribes are divided into genera, and the genera divided into species.  However, there are a number of tribes that are very difficult to distinguish morphologically.  These are grouped into a large, artificial tribe I call "Multitribe".  Multitribe is then divided into groups, and each group is then divided into genera.  The answers are in the order you would normally work through the keys.

Andropogoneae: Answers to key questions leading to this tribe. 
Mature inflorescence breaking into spikelet units consisting of a sessile fertile spikelet, a hairy pedicel with or without a sterile spikelet at tip, and a hairy rachis joint, all arising at the same point (a node) in specialized panicle branches called rames; NOT [Mature inflorescence, if breaking into units, then the units not as above]

Andropogon: Answers to key questions leading to this genus (in tribe Andropogoneae). 
Inflorescence with up to about 20 larger rames each composed of more than 3 spikelet units; spikelet units consisting of a sessile spikelet, a hairy pedicel terminating in a small or large spikelet, and a hairy rachis joint; pedicel and rachis joint wide and flat; NOT [Inflorescence with many, small rames each composed of 2-3 spikelet units; spikelet units consisting of a sessile spikelet, a hairy pedicel with no spikelet, and a hairy rachis joint; pedicel and rachis joint slender and terete]
Pedicellate spikelet about as large as sessile spikelet, well-developed; sheaths not strongly keeled; blades usually 4-10 mm broad; each peduncle in the inflorescence terminating in 2-7 (10) rames; rachis joint tip not cupulate; NOT [Pedicellate spikelet small, not well-developed; sheaths strongly keeled, blades usually less than 5 mm wide; each peduncle in the inflorescence terminating in a single rame; rachis joint tip cupulate]

Gerardii: Answers to key questions leading to this species (in genus Andropogon). 
Lemma awns 8-20 mm long, geniculate; rhizomes absent or short, the culms often densely tufted; rachis joint and pedicel of pedicellate spikelet sparsely to +/- densely villous, the hairs 2.2-4.2 mm long; inflorescence usually purplish; leaf blades +/- equally ridged on both surfaces, with every 4th ridge larger and more prominent than the intervening ridges; ligules usually < 2.5 (3) mm long; anthers usually < 3.8 mm long; plants scarcely glaucous; NOT [Lemma awns usually absent, if present then < 8 (10) mm long and not geniculate; rhizomes elongate, the culms not tufted; rachis joint and pedicel of pedicellate spikelet densely long-villous, the hairs 3.7-6.5 mm long; inflorescence usually strongly yellowish, or yellowish-gray; leaf blades more prominently ridged on adaxial than on abaxial surfaces, the ridges of each side +/- equal in prominence; ligules usually > (2.5) 3 mm long and up to 4.5 mm; anthers usually > 3.8 mm long; plants usually glaucous]