Setaria viridis
 
Green Foxtail

Spikelet Split Open

Crooked Lake Provincial Park
06-July-2023

This species is a member of tribe Paniceae which is characterized by a particular spikelet structure. A smaller lower glume subtends a sterile floret while on the opposite side a larger upper glume subtends a single fertile floret.  The base of the lower glume wraps around to the opposite side.

Note that in this species the upper glume is about as long as the spikelet and mostly covers the lemma surface of the fertile floret. In addition, the sterile floret lacks stamens and is equipped with a vestigial palea which is about 1/3 as long as the lemma, or absent.  The sterile floret palea appears to be absent in this specimen.

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.

Paniceae: Answers to key questions leading to this tribe. 
Mature inflorescence, if breaking into units, then the units not as below; NOT [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]
Spikelets usually dorsally compressed, appearing 1-flowered but containing 1 fertile floret and 1 sterile floret, the latter attached to the base of fertile floret opposite the upper glume, resembling the upper glume, and together with the upper glume enveloping the fertile floret; lower glumes minute (sometimes absent) to 3/4 as long as upper glumes and typically wrapping most of the way around the pedicel at base; fertile floret seed-like with chartaceous-indurate lemma and palea enclosing flower and fruit; disarticulation below the glumes with rare exceptions; NOT [Spikelets not as above; sterile florets if present, either located distal to the fertile floret(s) on the rachilla or paired and attached at the base of a single fertile floret, not paired with the upper glume as above; lemma and palea variously textured, enclosing the flower or not; disarticulation usually above the glumes]

Setaria: Answers to key questions leading to this genus (in tribe Paniceae). 
Spikelets with bristles attached in groups at base; panicle dense and spike-like; NOT [Spikelets lacking bristles but rachis and pedicels may have scattered, long, papillose-based hairs; panicle not spike-like]

Curtiseta: Answers to key questions leading to this species (in genus Setaria). 
Upper glumes about as long as the spikelet and mostly covering the inconspicuously transversely rugose lemma surface of the fertile floret; spikelets 1.8-2.2 mm long; bristles in groups of 1-3, usually green, purplish or tawny; leaf blades glabrous; leaf sheath margins long pubescent or ciliate distally; sterile florets lacking stamens, reduced to a lemma and a vestigial palea about 1/3 as long as lemma, or absent; NOT [Upper glumes about 1/2 as long as the spikelet and revealing the conspicuously transversely rugose lemma surface of the fertile floret; spikelets 2-3.5 mm long; bristles usually in groups of 4 or more, maturing to distinctive golden yellow to brownish yellow; leaf blades long villose at base on adaxial surface and sometimes pilose distally; leaf sheath margins not ciliate or pubescent distally; sterile florets usually staminate, their paleas well developed, about as long as the lemma]