1 Citation 335 Views 20 Downloads
In this study, we expanded Acer sect. Rubra Pax to include A. sect.
Hyptiocarpa Fang. Traditionally, section Rubra comprises two iconic
species, Acer rubrum Linnaeus (red maple) and A. saccharinum Linnaeus
(silver maple), of eastern North American forests as well as the rare
Japanese montane species, A. pycnanthum K. Koch. Section Hyptiocarpa
consists of A. laurinum Hasskarl and A. pinnatinervium Merrill, which
occur in subtropical and tropical regions of southwestern China to
southeast Asia. Here, we confirm prior phylogenetic results showing the
close relationship between sects. Rubra and Hyptiocarpa, and we use
scanning electron microscopy to demonstrate that leaves of species within
these sections have similar arrangements of cuticular waxes, which account
for the silvery color of their abaxial surfaces. We describe that the
sections also share labile sex expression; inflorescences that range from
compound racemose thyrses, to racemes or umbels and that may have
undergone evolutionary reduction; and several features of their fruits,
such as seed locules without keels, basal portion of wings straight, acute
attachment angle between mericarps, and production of some mericarps that
are seedless and partially developed at maturity. Our expansion of sect.
Rubra to include sect. Hyptiocarpa better elucidates the biogeographic and
evolutionary history of these species. Additionally, we show that A.
laurinum and A. pinnatinervium have intergrading morphology and are
probably synonymous, but we note that further studies are required to
conclude their taxonomic status.
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