keys to the vascular plants of east texas - Botanical Research ...

992 POACEAE/PANICUM
Marshes and South TX Plains, RICE is cultivated (e.g., Adair et al. 1973) and is occasionally a waif
or weed in moist soils. While less widely distributed than WHEAT, RICE feeds more people, being
the basic food for 1/2 or more of the world’s human population (Heiser 1990; Lu et al. 2000).
Together, RICE, WHEAT, and CORN provide ca. 45–50% of total human caloric intake (Chrispeels
& Sadava 1977; Mabberley 1997). Although RICE is usually cultivated in flooded fields (lowland
forms), there are some upland forms that are grown on dry land (Clayton & Renvoize 1976;
Mabberley 1997). RICE is used in a variety of ways: glutinous forms are used for puddings; nonglutinous
forms are widely used in curries, paella, risotto, etc.; the flour is used in cooking,
breakfast foods, and in commercial starch; some rice is fermented to produce beer or the wine
sake (Mabberley 1997). There are thousands of named and unnamed forms and variations of
this species (Tucker 1988). There can be great variability in awn length, from awnless to extremely
long (70 mm—Taylor & Taylor 17203, BRIT). I
PANICUM L. PANIC GRASS
Annuals or perennials with or without rhizomes; basal rosette leaves not developed, the basal
leaves few, usually withering by flowering time; ligule usually a membrane, often ciliate or
with a fringe of hairs; panicles much-branched, normally produced in one continuous period
of bloom, terminal or both terminal and lateral; spikelets awnless, with 2 florets; lower floret
sterile or staminate, with lemma resembling upper glume; upper floret perfect, with lemma
firm to hardened, glabrous, shiny, with margins inrolled; glumes usually both present, the first
typically shorter.
AThe generic delimitation of Panicum has been the focus of considerable and continuing controversy,
and the number of taxa recognized has varied widely. As treated in the broadest sense
by some authorities, it is a genus of � 600 species in 6 subgenera, making it the largest genus of
grasses (Zuloaga 1987) and one of the largest genera of flowering plants (Crins 1991). The segregate
genus Dichanthelium was recognized by Gould (1974), Gould and Clark (1978), Hatch
(2002), and others on the basis of such characters as an overwintering rosette of short broad
leaves, the C3 photosynthetic pathway, and spring chasmogamous inflorescences and small,
late-season, axillary, cleistogamous inflorescences. However, the overlap and blurring of these
and other characters in Central and South American taxa caused Zuloaga (1987) to question
the generic recognition of Dichanthelium. Nevertheless, it now seems clear that, based on cladistic
analyses of molecular and morphological data (Gómez-Martínez & Culham 2000;
Zuloaga et al. 2000; Giussani et al. 2001), Panicum in the broad sense is not a monophyletic
group. Unfortunately, there is at present insufficient data to definitively determine the best way
to divide the genus into segregates. Some authorities (e.g., Yatskievych 1999) are continuing to
recognize Panicum in the broad sense until further information is available. Other authorities
(e.g., Freckmann & Lelong 2003b) segregate Dichanthelium and Steinchisma but still retain a
diverse assemblage of species in Panicum. According to Freckmann and Lelong (2003b), recent
work “suggests that Panicum subg. Panicum is a monophyletic group that should have a rank
equivalent to Dichanthelium and Steinchisma. The two other subgenera…, subg. Agrostoidea
and subg. Phanopyrum, are not monophyletic, but the relationships of their species to other
members of Panicum sensu lato are not well enough understood to suggest a better treatment,
nor to justify the name changes a differing generic treatment would require.” Thus, until better
information is available, we are following Freckmann and Lelong (2003b) in recognizing a
rather broadly conceived (and possibly polyphyletic) Panicum while treating Dichanthelium
and Steinchisma at the generic level. As thus delimited, Panicum may have as many as 525 species;
Freckmann and Lelong (2003b) indicated that 72 are native or naturalized in North
America. It is a difficult group taxonomically because of complications ranging from apomixis
and polyploidy to hybridization and introgression (Freckmann & Lelong 2003b). Some species
here treated in Urochloa have previously been included in Panicum. This is illustrative of the