SáNCHEZ-KEN, JORGE GABRIEL.* AND LYNN G. CLARK. Department of Botany, Iowa State University, 353 Bessey Hall, Ames, IA, 50011-1020. - Overview of the subfamily Centothecoideae (Poaceae).
The subfamily Centothecoideae s.s, distributed worldwide in the
tropical and subtemperate regions, comprises 10 genera (Bromuniola,
Calderonella, Centotheca, Chasmanthium, Chevalierella, Lophatherum,
Megastachya, Orthoclada, Pohlidium and Zeugites). It was defined
originally by embryo formula (P+PP and F+PP), tessellation of the
leaf-blades, pseudopetiolate leaves, small herbaceous habit, and
forest habitat, as well as by the differentiation of the mesophyll
into palisade and spongy tissue, but its cohesiveness was questionable
and its relationships were uncertain. In the last two decades, certain
other genera (Cyperochloa, Danthoniopsis, Gouldochloa, Gynerium,
Spartochloa, and Thysanolaena) have been segregated from other
subfamilies and placed in or suggested as members of the centothecoid
clade; a sister relationship between the centothecoids in the broad
sense (including these genera) and the Panicoideae also has been
inferred. These findings were based mainly on molecular data and some
morphological data also, although at present there is no morphological
synapomorphy that supports the centothecoids as monophyletic.
Consequently, the position of these genera with respect to the
centothecoids, and the circumscription of the centothecoid clade
itself, remain uncertain. We present a preliminary morphological and
anatomical comparison of the Centothecoideae s.s. and the putatively
related genera, as well as a preliminary phylogenetic analysis using
molecular and morphological data. According to the morphoanatomical
data, leaf anatomy in cross section, the venation of the leaf blades,
and the arrangement of the unisexual florets in the spikelets are
likely to be the most informative features.
Key words: Centothecoideae, informative characters, monophyly, sister group