CAMPBELL, LISA M.1*, DENNIS WM. STEVENSON1, JERROLD I DAVIS2, and CHRISTOPHER R. HARDY1. 1New York Botanical Garden, Bronx, NY 10458; 2L. H. Bailey Hortorium, Cornell University, Ithaca, NY 14853. - Alternative hypotheses for the systematic placement of Mayaca.
Mayaca is a monogeneric family of aquatic herbs with
approximately four species in subtropical to tropical America and west
Africa. The reduced size and adaptation to the aquatic habit has made
the placement of Mayaca within the commelinid clade difficult.
In traditional systems of classification it has been suggested that
this genus is related to Commelinaceae based on poricidal anther
dehiscence and the operculate seeds, or to Xyridaceae based on
parietal placentation and orthotropus, tenuinucellate ovules. However,
subsequent data has shown that seed operculum development differs
between Mayaca and Commelinaceae, and that Xyridaceae are
variable in ovule development and orientation, as well as
placentation. Despite this, Mayaca and Xyridaceae share an
exothecium, a feature not known to occur in Commelinaceae. Recent
analyses of ndhF and rbcL sequence data allied Mayaca to
Bromeliaceae and Rapateaceae; the latter also have poricidal anther
dehiscence. In our on-going analysis of rbcL, atpA, and cob sequence
data representing all orders of monocots, Mayaca has been
placed in a variety of positions, appearing either as sister to
Eriocaulaceae or to Xyridaceae. These alternative hypotheses will be
evaluated with respect to morphological data.
Key words: Bromeliaceae, commelinids, Eriocaulaceae, Mayaca, Rapateaceae, Xyridaceae