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

1042 POACEAE/SACCHARUM
of each spikelet with a long awn (awn absent in S. officinarum); palea of fertile floret ca. 1/2 as
long as lemma; palea of sterile floret absent; stamens usually 2 (3 in S. officinarum).
AThe genus, as treated here including Erianthus, comprises 35–40 species (Webster & Shaw
1995; Mabberley 1997; Webster 2003) of tropical and warm areas of the world. The center of diversity,
with ca. 25 species, is tropical Asia (Webster & Shaw 1995). Like all members of the
Andropogoneae, Saccharum is characterized by C4 photosynthesis (Kellogg 2000a). The traditional
segregation of awned species as Erianthus and awnless species as Saccharum has been
described as “wholly artificial” (Clayton & Renvoize 1986). Some authorities (e.g., Daniels &
Roach 1987; Whalen 1991) disagree, and they treat Saccharum more narrowly, including only
SUGARCANE and its immediate relatives (only 5 species), with the rest of the species segregated
into Erianthus. However, Burner and Webster (1994) successfully obtained hybrids between
Erianthus species and SUGARCANE, and Burner et al. (1997) found North American Erianthus to
be genetically similar to SUGARCANE cultivars. Nonetheless, recent molecular research (Dillon
et al. 2001) raises the possibility that Saccharum officinarum (SUGARCANE) is derived from
within Sorghum, while Erianthus appears more closely related to Zea; such results argue for the
separate recognition of Erianthus. Likewise, Nair et al. (1999) found “considerable divergence”
between Erianthus and Saccharum. Until such issues are resolved, we are following most recent
authorities (e.g., Hatch 2002; Webster 2003) in treating Saccharum broadly, to include
Erianthus. Saccharum is related to Eulalia, Imperata, and Miscanthus, and it also will hybridize
with Sorghum (Gupta et al. 1978). Webster and Shaw (1995) indicated that the “single most
reliable character for distinguishing among the [North American] taxa is the length of the callus
hairs relative to spikelet length.” The long callus hairs may aid in dispersal by wind (Webster
& Shaw 1995). The economically most important member of the genus is S. officinarum L.
(SUGARCANE), which is the source of ca. 1/2 of the world’s sugar. � Saccharum spontaneum L.,
WILD SUGARCANE, known in the U.S. from HI and PR, is a federal noxious weed (Kartesz 1999;
USDA Natural Resources Conservation Service 2002). The following treatment draws heavily
on Webster and Shaw (1995). (Latin: saccharum, sugar, referring to the sweet sap) (subfamily
Panicoideae, tribe Andropogoneae)
REFERENCES: Mukherjee 1958; Daniels & Roach 1987; Reveal et al. 1989; Whalen 1991; Gandhi &
Dutton 1993; Burner & Webster 1994; Webster & Shaw 1995; Nair et al. 1999; Weakley 2000;
Webster 2003.
1. Lemma of fertile (= upper) floret without an awn; anthers 3 per floret; introduced cultivated
species rarely if ever escaping in East TX ____________________________________________ S. officinarum
1. Lemma of fertile floret with a conspicuous awn; anthers 2 per floret; native species widespread
in East TX.
2. Awn of lemma of fertile floret spiraled at base (the spiral is easily visible to the naked eye).
3. Callus hairs (= conspicuous whorl of hairs attached directly below spikelet) equal to or
shorter than spikelet, 3–6.5 mm long, white to straw-colored or brownish; peduncle (=
stalk of inflorescence) glabrous or with sparse pubescence just below inflorescence _____ S. brevibarbe
3. Callus hairs longer than spikelet, ca. 9–14 mm long, silvery or purplish tinged; peduncle
with conspicuous, appressed, long pubescence just below inflorescence ___________ S. alopecuroides
2. Awn of lemma of fertile floret not spiraled at base.
4. Callus hairs longer than spikelet, (7–)15–20(–25) mm long; lemma of fertile floret with a
single vein; peduncle with conspicuous, appressed, long pubescence just below inflorescence;
leaf blades with sparse long pubescence on upper surface ____________________ S. giganteum
4. Callus hairs equal to or shorter than spikelet, 0–6.5 mm long or absent; lemma of fertile
floret with 3 veins; peduncle glabrous or with sparse pubescence; leaf blades glabrous on
upper surface.
5. Callus glabrous or with hairs 2 mm long or less; main branches of inflorescence glabrous,
appressed, the inflorescence thus only 1–3 cm wide ________________________ S. baldwinii