Morphology and Leaf Blade Anatomy Suggest a Close Relationship Between Bouteloua aristidoides and B. (Chondrosium) eriopoda (Gramineae: Chloridoideae)

Abstract

Bouteloua aristidoides and B. eriopoda (Gramineae: Chloridoideae) have long been resident in separate subgenera or genera, Bouiteloua s. str. and Chondrosium, respectively, because they differ in number of branches per inflorescence, branch length, number of spikelets per branch, and branches deciduous versus persistent. However, the species are similar in spikelet orientation and form, including lodicules and the abax- ial epidermis of the fertile lemma, and in transverse structure of the leaf blade. These two species, together with B. annua and B. eriostachya (first described as a variety of B. eriopoda), uniquely share a suite of morpho- logical and leaf blade anatomical characteristics. A close relationship among these four species is hypothe- sized. In light of these findings, recognition of Chondrosium either as a subgenus or genus is discouraged. Other findings include much variation in anther and stigma size and confirmation of cleistogamy in B. aristi- doides, cleistogamy and chasmogamy in B. annua, chasmogamy in B. eriopoda and B. eriostachya, inflorescence branch abscission in B. eriostachya, spikelet disarticulation preceding branch abscission in B. anntia and some B. aristidoides, a thin outer wall of lemma short cells, and a predicted NAD-ME pathway of C4 photosynthesis from leaf blade structure. Divergence (speciation) of B. aristidoides may have been associated with a shift to annuality and autogamy to avoid drought, which predisposed the species for success in disturbed habitats. These characteristics plus epizoochory likely account for its wide, amphitropical distribution.