RUDALL, PAULA J. Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK. - Floral morphology of Asparagales: unique structures and iterative evolutionary themes.
Although relationships between the lilioid and commelinoid monocot
orders are still unresolved, there is emerging consensus regarding
family relationships within these orders, prompting a reevaluation of
character evolution in these groups. In particular, relationships are
now fairly well established between the basal clades of the large
monocot order Asparagales (the asparagoid lilies), based mainly on
molecular data. Asparagales comprise a 'higher asparagoid' clade and a
'lower asparagoid' grade, which includes some small families such as
Tecophilaeaceae, the monogeneric Eurasian family Ixioliriaceae, and
the monotypic South African genus Lanaria (Lanariaceae), plus
some large, cosmopolitan families such as Iridaceae and Orchidaceae,
the latter putatively sister to all other Asparagales. A revised
morphological cladistic analysis of Asparagales was undertaken to
evaluate character support for these hypotheses of relationships and
assess character evolution in Asparagales. Synapomorphies for the
order include the presence of simultaneous microsporogenesis,
epigynous ovaries, and phytomelan in the seed coat, but there are some
reversals in these characters, especially in the higher asparagoids. A
major reversal to hypogyny in the higher asparagoids and their sister
clade is concomitant with the presence of infralocular septal
nectaries in the latter. Recurrent evolutionary themes in floral
structure of lower asparagoids include loss or reduction of either one
stamen whorl (in actinomorphic taxa) or selected stamens (in
zygomorphic taxa), and various other androecial and gynoecial
modifications, such as centrifixed anthers, presence of a gynostemium
(primarily an orchid character), and unilocular ovaries.
Key words: Asparagales, evolution, floral anatomy, systematics