Plant Genera


Family Code: POACEA
Genus Code: ANDRO2
Genus CN: bluestem
Genus Authority: L.
Genus Summary: A genus of about 100-110 species, mainly tropical. Campbell's work (1983, et seq.) has greatly clarified the taxonomy of Andropogon in e. North America. Great confusion and disagreement were previously the rule in dealing with the A. virginicus-A. glomeratus complex. Campbell's careful morphologic work has provided workable technical characters which distinguish the taxa he recognizes. I have generally followed Campbell (1983, et seq.) in his circumscriptions of taxa, but have differed in decisions of rank; see Weakley et al. (2011) for discussion. Taxa differing in numerous morphologic characters, with different (though overlapping) geographic ranges, with different ecological preferences (often rather narrowly segregated by hydrology), and (when they do occur in proximity to one another) showing little or no sign of introgression or hybridization are probably better treated as biological species. Thus, I have treated a number of Campbell's varieties as species. Several of his "variants" also warrant taxonomic recognition, at varietal or specific rank (Campbell 1986; Weakley et al. 2011).
Genus Identification: Identification notes: A thorough understanding of the architecture of the inflorescences of Andropogon is necessary in order to identify them successfully. The parts will be described, beginning from the apex of a branch of the inflorescence. Spikelets occur in pairs, the sessile spikelet (usually just referred to as the spikelet) and the pedicelled spikelet, which is usually vestigial or absent (except in A. gerardi) and sterile (except in A. gerardi, where it is staminate). The first or lower glume of the sessile spikelet has two keels, and the presence and location of antrorse prickle hairs (scabrousness) is an important character in the A. glomeratus complex. The length of the sessile spikelet is an important character; it should be measured exclusive of the awn, borne at the apex of the lemma. Awn length is also a useful taxonomic character. The pedicelled spikelet is borne on the pedicel, which is attached at the base of the sessile spikelet and typically angles away from it at about a 45 degree angle. The rachis internode extends from the base of one sessile spikelet to the next sessile spikelet above, breaking apart (upon dehiscence) just below the next spikelet and remaining attached to the sessile spikelet below. The dispersal unit consists of a sessile spikelet sitting in the V shape formed by (on one side) the pedicel and pedicelled spikelet and (on the other side) the rachis internode. Both the pedicel and the rachis internode are usually pubescent with long hairs, and the color of those hairs and their distribution are useful characters.
Genus References: Campbell (1983)=Z; Campbell in FNA (2003a); Weakley et al. (2011)=Y. Key adapted in part from Z.
Last Updated: 2019-11-29
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