COLUMBUS, J. TRAVIS* and ERIC H. ROALSON. Rancho Santa Ana Botanic Garden, 1500 N. College Ave., Claremont, California 91711. - Phylogenetics of Hilaria and Pleuraphis (Gramineae: Chloridoideae).
Cladistic parsimony analysis of internal transcribed spacer (ITS)
region nrDNA sequences indicates a sister relationship between the
North American chloridoid grass genera Hilaria (8 or 9 spp.)
and Pleuraphis (3 spp.). Introgression between P.
jamesii and P. rigida, previously inferred from morphology,
is evidenced in the ITS phylogeny. Hilaria is composed of three
main lineages: (A) H. semplei, (B) H. belangeri, H.
cenchroides, and H. swallenii, and (C) H. annua,
H. ciliata, H. hintonii, and one, possibly two,
undescribed species. Characters from morphology and leaf blade
transectional anatomy support the Hilaria and Pleuraphis
clades and the three lineages within Hilaria. However, species
circumscription within Hilaria clade B remains uncertain. Much
variation exists in the leaf blade structure of these genera.
Pleuraphis possesses a suite of anatomical and cytological
features that suggests the NAD malic enzyme (NAD-ME) photosynthetic
pathway. Hilaria species in clade C exhibit a blade structure
indicative of the PEP carboxykinase (PCK) pathway, whereas H.
semplei and species in clade B are intermediate between clade C
and Pleuraphis with respect to the anatomical/cytological
characters that predict the subtype of C4 photosynthesis.
Key words: Chloridoideae, Gramineae, Hilaria, leaf anatomy, phylogenetics, Pleuraphis