2. Leitneria
Chapm. (corkwood)
Contributed by Alan Whittemore
One species (but
see the discussion below), southeastern United States.
As noted above
in the discussion of the family, Leitneria was treated traditionally as
a monospecific family of uncertain taxonomic affinity (Cronquist, 1981, 1991),
the only angiosperm family entirely endemic to the United States. This was in
large part because the highly reduced flowers of L. floridana offer few
clues as to relationships with other families. It was initially surprising when
molecular data suggested that Leitneria was, in fact, a highly modified
member of the Simaroubaceae in which floral reduction and condensation of
inflorescences correlated with a shift from insect pollination to wind
pollination. Also, most Simaroubaceae are aromatic, at least when tissue is
crushed or bruised, but not Leitneria. Features supporting the genetic
data turn out to be mostly nonmorphological, for example that Leitneria
produces secretory canals. Other evidence supporting a relationship between Leitneria
and the Simaroubaceae comes from serological studies of pollen proteins (this
involves injecting protein samples into laboratory animals to produce antisera,
which are then isolated and tested for their relative reactivity to protein
samples from other plant species) by Petersen and Fairbrothers (1983), as well
as comparative embryological research (Tobe, 2011).