Plants annual or perennial; synoecious, monoecious, or dioecious; primarily herbaceous, habit varied. Culms annual, usually solid, sometimes somewhat woody, sometimes decumbent, often branched above the base. Leaves distichous; sheaths usually open; auricles usually absent; abaxial ligules usually absent, occasionally present as a line of hairs; adaxial ligules membranous, sometimes also ciliate, or of hairs, sometimes absent; blades sometimes pseudopetiolate; mesophyll radiate or non-radiate; adaxial palisade layer absent; fusoid cells usually absent; arm cells usually absent; kranz anatomy absent or present; midribs usually simple, rarely complex; adaxial bulliform cells present; stomata with triangular or dome-shaped subsidiary cells; bicellular microhairs usually present, with a long, narrow distal cell; papillae absent or present. Inflorescences ebracteate (Paniceae) or bracteate (most Andropogoneae) panicles, racemes, spikes, or complex arrangements of rames (in the Andropogoneae), usually bisexual, sometimes unisexual; disarticulation usually below the glumes, frequently in the secondary and higher order axes of the inflorescences. Spikelets bisexual or unisexual, frequently paired or in triplets, the members of each unit usually with pedicels of different lengths or 1 spikelet sessile. Glumes usually 2, equal or unequal, shorter or longer than the adjacent florets, sometimes exceeding the distal florets; florets 2(-4), usually dorsally compressed, sometimes terete or laterally compressed; lower florets sterile or staminate, frequently reduced to a lemma; upper florets usually bisexual; lemmas hyaline to coriaceous, lacking uncinate hairs, often terminally awned; awns single; paleas of bisexual florets well-developed, reduced, or absent; lodicules usually 2, sometimes absent, cuneate, free, fleshy, usually glabrous; anthers 1-3; ovaries usually glabrous; haustorial synergids absent; style branches 2, free and close or fused at the base. Caryopses: hila usually punctate; endosperm hard, without lipid; starch grains simple; embryos large in relation to the caryopses, usually waisted; epiblasts usually absent; scutellar cleft present; mesocotyl internode elongated; embryonic leaf margins usually overlapping, rarely just meeting, x = 5, (7), 9, 10, (12), (14).

Discussion

The subfamily Panicoideae is most abundant in tropical and subtropical regions, particularly mesic portions of such regions, but several species grow in temperate regions of the world. Within the Flora region, the Panicoideae are represented by 59 genera and 364 species. They are most abundant in the eastern United States (Barkworth and Capels 2000). Photosynthesis may be either C3 or C4. All three pathways are found in the subfamily, but the PCK and NAD-ME variants appear to have evolved only once, while the NADP-ME pathways seems to have evolved several different times (Giussani et al. 2001).

The Panicoideae were first recognized as a distinct unit by Brown (1814), earlier than any of the other subfamilial taxa of the Poaceae. Its early recognition is undoubtedly attributable to its distinctive spikelets. Recognition of the tribe Gynerieae is recent (Sanchez-Ken and Clark 2001) and its placement in the Panicoideae, rather than the Centothecoideae, should be regarded as tentative.

Spikelets with two florets are found in many other subfamilies, but rarely do they follow the pattern of the lower floret being sterile or staminate and the upper floret bisexual. Development of unisexual florets within the Panicoideae appears to be consistent across the subfamily (LeRoux and Kellogg 1999), but differs from that in the Ehrhartoideae (Zaitcheck et al. 2000).

The Paniceae and Andropogoneae have their conventional interpretation in this Flora, so far as the North American taxa are concerned. Molecular studies, however, while strongly supporting the monophyly of the Andropogoneae, show the Paniceae to be paraphyletic, with two distinct clades. In one of these clades, most taxa have a chromosome base number of x = 9, but some have x = 10, and the taxa are pan-tropical in origin. The taxa in the other clade, with one exception, have a chromosome base number of x = 10 and are American in origin. This latter clade is sister to the Andropogoneae, which also have a chromosome base number of x = 10 (Gomez-Martinez and Culham 2000; Giussanni et al. 2001; Barber et al. 2002).

Selected References

Barber, J.C., S.A. Aliscioni, L.M. Giussani, J.D. Noll, M.R. Duvall, and E.A. Kellogg. 2002. Combined analyses of three independent datasets to investigate phytogeny of Poaceae subfamily Panicoideae. [Abstract.] http://www.botany2002.org/

Barkworth, M.E. and K.M. Capels. 2000. The Poaceae in North America: A geographic perspective. Pp. 327-346 in S.W.L. Jacobs and J. Everett (eds.). Grasses: Systematics and Evolution. International Symposium on Grass Systematics and Evolution (3rd:1998). CSIRO Publishing, Collingwood, Victoria, Australia. 408 pp.

Brown, R. 1814. General remarks, geographical and systematical, on the botany of Terra Australis. Pp. 533-613 in M. Flinders (ed.). A Voyage to Terra Australis, vol. 2. G. and W. Nicol, London, England. 613 pp.

Giussani, L.M., J.H. Cota-Sanchez, F.O. Zuloaga, and E.A. Kellogg. 2001. A molecular phytogeny of the grass subfamily Panicoideae (Poaceae) shows multiple origins of C4 photosynthesis. Amer. J. Bot. 88:1993-2001

Gomez-Martinez, R. and A. Culham. 2000. Phytogeny of the subfamily Panicoideae with emphasis on the tribe Paniceae: Evidence from the trnL-F cpDNA region. Pp. 136-140 in S.W.L. Jacobs and J. Everett (eds.). Grasses: Systematics and Evolution. International Symposium on Grass Systematics and Evolution (3rd:1998). CSIRO Publishing, Collingwood, Victoria, Australia. 408 pp.

Grass Phylogeny Working Group. 2001. Phytogeny and subfamilial classification of the grasses (Poaceae). Ann. Missouri Bot. Gard. 88:373^-57

Hilu, K.W., L.A. Alice and H. Liang. 1999. Phytogeny of the Poaceae inferred from matK sequences. Ann. Missouri Bot. Gard. 86:835-851

Kellogg, E.A. 2000. Molecular and morphological evolution in the Andropogoneae. Pp. 149-158 in S.W.L. Jacobs and J. Everett (eds.). Grasses: Systematics and Evolution. International Symposium on Grass Systematics and Evolution (3rd:1998). CSIRO Publishing, Collingwood, Victoria, Australia. 408 pp.

Le Roux, L.G. and E.A. Kellogg. 1999. Floral development and the formation of unisexual spikelets in the Andropogoneae (Poaceae). Amer. J. Bot. 86:354-366

Sanchez-Ken, J.G. and L.G. Clark. 2001. Gynerieae, a new neotropical tribe of grasses (Poaceae). Novon 11:350-352

Zaitcheck, B.F., L.G. Le Roux, and E.A. Kellogg. 2000. Development of male flowers in Zizania aquatica (North American wild-rice Gramineae). Int. J. PI. Sci. 161:345-351.

Lower Taxa

Poaceae tribe Andropogoneae, Poaceae tribe Gynerieae, Poaceae tribe Paniceae

Key

1	Blades of leaves on the lower 1/2 of the culms disarticulating from the sheaths; plants 2-15 m tall, unisexual, without axillary inflorescences; blades with midribs 5-15 mm wide	Gynerieae
1	Blades of most or all cauline leaves remaining attached to the sheaths; plants 0.05-6 m tall, usually bisexual, sometimes with unisexual inflorescences, often with axillary inflorescences; blades with midribs 0.2-5 mm wide.	> 2
2	Glumes usually conspicuously unequal; lower glumes usually greatly exceeded by the upper florets; upper glumes from subequal to longer than the distal florets; lemmas of the upper florets usually coriaceous to indurate; disarticulation usually beneath the glumes, not in the axes of the inflorescence branches	Paniceae
2	Glumes usually subequal, usually exceeding and concealing the florets; lemmas of the upper florets hyaline to membranous; disarticulation frequently in the axes of the inflorescence branches	Andropogoneae