Family Poaceae - Subfamily Chloridoideae

· warm season (C4) grasses of arid habitats (diverse in desert regions of the world), and most genera with a predominantly hairy ligule (we will see at least two exceptions).

· distinct morphologies often used in the paleo-ecological literature to infer warm temperate habitats – silica bodies that are saddle-shaped, and leaves with kranz-anatomy as well as an epidermis with microhairs having the terminal cell distinctly enlarged (figures from L. Watson and M. J. Dallwitz. 1988. Grass Genera of the World. Canberra, Australia: Australian National University Printing Service).

· the base chromosome number is mostly x=10.

Tribe Chlorideae

1. inflorescence comprising one-sided spikes and these laterally or digitately arranged. 2. mostly just the first floret of a spikelet is fertile, if any rudimentary (sterile and modified) florets are present, these occur above the fertile floret; rarely are there several fertile florets per spikelet.

· Bouteloua: laterally arranged secund spikes divergent to reflexed from the main rachis, rudimentary florets distinct and bearing 1 or 3 awns depending on the species.

· Buchloe: dioecious perennial, mat-forming, the pistillate spikelets clustered several together in a burr-like structure formed from the indurated second glume and subtending inflorescence rachis of each spikelet, staminate plants bearing spikelets similar to those of Bouteloua.

· Cynodon: digitately arranged secund spikes, rhizomatous and stoloniferous, spikelets strongly laterally compressed and with a distinctly visible single floret (unlike the superficially similar Paspalum and Digitaria of the tribe Paniceae).

· Eleusine: digitately arranged secund spikes like Cynodon, but the spikelets are with several to many florets.

· Spartina: very similar to Bouteloua but the one-sided spikes are appressed to the main inflorescence rachis and the spikelets contain only one fertile floret with no rudimentary florets.

· Schedonnardus: like Bouteloua in having laterally arranged one-sided spikes, but differing in having long lateral spikes 4-10 cm long and that have the spikelets closely appressed to the rachis of the lateral spike.

Tribe Aeluropodeae

1. distichous leaves with usually sharp tips. 2. dioecious, pistillate and staminate spikelets separated on different individuals. 3. very stout woody rhizomes extensively developing. 4. collar with distinct long straight hairs (evident on culms at least before the spikelets are produced).

· Distichlis: because this is the only genus of the tribe in Montana, the same characters listed for the tribe also distinguish the genus. Three other genera belong to the tribe and are found at dry sandy sites (interior and coastal sand dunes) in the very southern latitudes of the United States and southward into Latin-America. All genera of Aeluropodeae have 1-3 species each and it is unclear how Distichlis is distinguished from the other genera of the tribe.

Tribe Eragrosteae

1. There is no distinctive morphological traits of this tribe, and for the purposes of this course, it is characterized as a group of grass genera of subfamily Chloridoideae that lack the traits of the other tribes, namely Chlorideae and Aeluropodeae. This tribe will be most confused with genera of Aveneae and Poeae of the subfamily Pooideae. Because all Pooideae are cool season grasses and all Chloridoideae are warm season, the habitat of the genera of Eragrosteae is expected to be very different from that of the genera of Pooideae. Also, lemmas with 3 distinct veins and ligules composed of mostly hairs are common in Chloridoideae (including Eragrosteae) but very uncommon or absent in Pooideae (including Aveneae and Poeae). So these traits combined can distinguish genera of Eragrosteae that superficially appear to be a member of Aveneae or Poeae.

· Calamovilfa: single floret bearing long hairs and enveloped by large glumes (thus like Calamogrostis), but with hairy ligule, wiry leaves, inhabiting dry sites.

· Eragrostis: many florets per spikelet (8-50+), persistent paleas, diaspore is the achene.

· Muhlenbergia: membraneous ligule (the only genus in Eragrosteae), lemma distinctly 3-nerved in nearly all species; fruit is a caryopsis.

· Munroa: mat-forming, spiklets clusters in leaf sheaths (like pistillate spikelets of Buchloe, but spikelets not coalescing into a burr).

· Sporobolus: like Muhlenbergia in having 1 floret per spikelet, but the ligule is hairy, the lemma is 1-nerved, and the fruit is often an achene. Also, the first glume is usually distinctly shorter than the second in Sporobolus, as compared to Muhlenbergia or even Agrostis (of tribe Aveneae).

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