(excl. Dichanthelium (Hitchc. et Chase) Gould, Zuloagaea Bess)
Panicum is a very large genus of ca. 170 species, mostly in tropical and warm-temperate regions. None is native in Belgium. It formerly accommodated most panicoid grasses that now have been transferred to related genera like Paspalum, Setaria,… but surely is still polyphyletic. Molecular research further reduced the number of species in Panicum s.l. (see Aliscioni & al. 2003 and Zuloaga & al. 2018 for additional information on the molecular phylogeny of Panicum). In the present treatment subgenus Dichanthelium is accepted as a genus of its own. Likewise, the genus Zuloagaea, with its single species Z. bulbosa (Kunth) Bess (syn.: Panicum bulbosum Kunth), was recently segregated (Bess & al. 2006). It turned out to be more closely related to Cenchrus, Pennisetum and Setaria (the so-called “bristle-clade”) than to Panicum. It was formerly recorded once as a wool alien in the Vesdre valley (Verloove 2001).
The genus is pantropical with some species extending to more temperate regions in North America. Under influence of man, several species have much enlarged their distribution range (as agricultural weeds or as minor crops).
1 Lower floret staminate, palea of the lower floret well developed. Plants annual or perennial === 2
1 Lower floret neuter, palea of the lower floret absent, poorly or well developed. Plants always annual === 4
2 Lower glume ¼-1/5 of spikelet length. Spikelets usually obtuse at apex (to bluntly acute). Plant annual, weedy === P. schinzii p.p.
2 Lower glume 1/3-2/3 of spikelet length. Spikelets acute-acuminate at apex. Plant perennial, a garden escape === 3
3 Lower glume 1-1,5 mm long, less than ½ as long as spikelet, 1-3-veined. Lower palea not hastate-lobed. Spikelets not markedly gaping at maturity, rarely more than 3 mm long === P. coloratum
3 Lower glume 1,8-3,2 mm long, more than ½ as long as spikelet, 5-9-veined. Lower palea hastate-lobed. Spikelets strongly gaping at maturity, rarely less than 3 mm long === P. virgatum
4 Lower glume ¼-1/5 of spikelet length. Leaf sheaths glabrous (but young sheaths very rarely slightly hairy) === 5
4 Lower glume more than ½ of spikelet length. Leaf sheaths always distinctly hairy === 7
5 Palea of the lower floret absent. Spikelets ca. 2,5 mm long (on average) === P. chloroticum
5 Palea of the lower floret present, of variable length. Spikelets ca. 3,5 mm long (on average) === 6
6 Spikelets obtuse to bluntly acute at apex. Palea of the lower floret (almost) equal in length and width to upper lemma === P. schinzii p.p.
6 Spikelets acute at apex. Palea of the lower floret much narrower and usually shorter than upper lemma === P. dichotomiflorum
7 Panicle usually more than ½ the length of the entire plant === 8
7 Panicle less than ½ the length of the entire plant === 9
8 Palea of the lower floret well developed, at least ½ the length of the upper lemma, 1-1,5 mm long. Upper lemma plump (width 1,1-1,3 mm), dark brown at maturity with two conspicuous, lunate swellings at base. Culms usually stout, panicle soon exserted from the leaf base === P. hillmanii
8 Palea of the lower floret absent (rarely vestigial and then at most 0,3 mm long). Upper lemma elliptic (width 0,5-0,9 mm), yellowish-brown at maturity, without swellings at base. Culms often more slender, panicle usually long remaining inserted in the leaf base === P. capillare
9 Spikelets not over 3,3 mm long. Panicle erect === P. hirticaule
9 Spikelets 4,5-5,5 mm long. Panicle usually drooping, rarely more erect === P. miliaceum
Additional aliens: Panicum antidotale Retz. (syn.: P. miliare Lam.) (As., wool alien), P. decompositum R. Brown (Austr., wool alien) and P. laevinode Lindl. (syn.: P. whitei J.M. Black) (Austr., wool alien). Panicum bulbosum Kunth, formerly recorded as a wool alien in the Vesdre valley (see Verloove 2001), is now accommodated in a separate genus (as Zuloagaea bulbosa (Kunth) Bess).
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