Pollination biology of basal angiosperms (ANITA grade)

Abstract

The first three branches of the angiosperm phylogenetic tree consist of eight families with ∼201 species of plants (the ANITA grade). The oldest flower fossil for the group is dated to the Early Cretaceous (115-125 Mya) and identified to the Nymphaeales. The flowers of extant plants in the ANITA grade are small, and pollen is the edible reward (rarely nectar or starch bodies). Unlike many gymnosperms that secrete "pollination drops," ANITA-grade members examined thus far have a dry-type stigma. Copious secretions of stigmatic fluid are restricted to the Nymphaeales, but this is not nectar. Floral odors, floral thermogenesis (a resource), and colored tepals attract insects in deceit-based pollination syndromes throughout the first three branches of the phylogenetic tree. Self-incompatibility and an extragynoecial compitum occur in some species in the Austrobaileyales. Flies are primary pollinators in six families (10 genera). Beetles are pollinators in five families varying in importance as primary (exclusive) to secondary vectors of pollen. Bees are major pollinators only in the Nymphaeaceae. It is hypothesized that large flowers in Nymphaeaceae are the result of the interaction of heat, floral odors, and colored tepals to trap insects to increase fitness.

Morphology, viability, and germinability of pollen from two forms of Nymphaea nouchali var. versicolor, a day-blooming waterlily

“…Interestingly, the sucrose concentration in the stigmatic fluids of open flowers of Nymphaea spp. is likely to be lower than 5% and therefore would not pose a problem for pollen germination under natural conditions 19 . The pollen germination result obtained in the present study was obviously in contrast to that of other studies showing that 5-20% sucrose enhanced in vitro pollen germination 20 .…”

Pollination of Myristica and Other Nutmegs in Natural Populations

“…The "mistake" pollination of nutmegs is quite different from the pollination syndromes found in other families of the Magnoliales (Annonaceae, Degeneriaceae, Eupomatiaceae, Himantandraceae, Magnoliaceae and Myristicaceae) in the topology of Soltis et al [1,25,26,[63][64][65][66][67]. In terms of floral organization, the nutmegs with small, unisexual, few-parted flowers and mistake pollination have more in common with some members of some ANA grade families (e.g., Amborellaceae), where unisexual flowers, pollen rewards, and food deceit are fairly common biologies [35]. A generalist entomophily involving beetles, thrips, micropterigid moths, as well as dipterans, and hymenopterans was proposed for ancestral angiosperms [68], and as more of the nutmegs are studied, this list is likely to describe their associated pollinators.…”

“…For plants in the ANA grade (the three basal lineages of angiosperms), beetles, bees, and flies are important pollinators, and pollen rewards and floral deceit are common [35,36]. Nutmegs not only have these features, but their small flower size, concave and enclosing perianths with small entrances, scented flowers, and nocturnal flowering, are all associated with beetle, thrip, and/or fly pollinators [34,[35][36][37]. The floral biology, the nature of pollination, and important pollinators of members of the nutmeg family have been elucidated by field studies of natural populations of several species of Myristica, and a review of these findings will form the basis for this report, although as we shall demonstrate, the nutmeg family remains under studied 45 years after Flach's 1966 report [22] summarizing knowledge of commercial nutmeg reproduction, during which time the study of tropical organisms has blossomed.…”

Morphological strategies of Cabomba (Cabombaceae), a genus of aquatic plants

“…Within the ANITA grade, the production of nectar has been detected in four families (Cabombaceae, Nymphaeaceae, Schisan- draceae and Illiciaceae), providing compelling evidence of cross-pollination (Thien et al 2009).…”