Evolution of pollination system and characters of stigmas in Najadales

Abstract

Abstract:

Diverse ways of pollination, including aerial, epihydrophilous and hypohy-

drophilous ones occur in the Najadales. Although the knowledge of pollination biology in this

order has been largely accumulated in recent years, most researchers ignored the role of stig-

mas in the pollination process. Based on the previous works, we supplemented observations

on stigmatic characters and pollination mechanism in nine species from four families. The

flowers of Aponogeton lakhonensis ( Aponogetonaceae ), Triglochin palustre ( Juncagi-

naceae), Potamogeton crispus, P. distinctus, P. gramineus, P. pectinatus, P. perfo-

liatus, P. pusillus (Potamogetonaceae), are all found to open above or on water surface.

Stigmas in these species have a large surface area. Correspondingly, the pollen grains are all

found to be globular. Of the eight species, except for P. pectinatus and P. pusillus, the

remaining six obviously expose their stigmas out of the perianth. Another species , Najas

marina (Najadaceae), has filiform stigmas and ellipsoidal pollen grains which can germinate

in water before being transferred onto stigmas in natural conditions. Pollination takes place in

this species strictly under water. The characters of pollen and stigmas could be divided into

two types, and the pollination system is of two kinds of mechanisms of stigmas capturing

pollen in the Najadales. The species with globular pollen grains have wide, large stigmas

while those producing filiform or precocious pollen grains, which are likely to be captured by

stigmas during the pollen dispersal by water currents, normally have filiform stigmas. It is

inferred that various water stresses might have resulted in the diversification of pollination

system in the Najadales.

Key words: Najadales, Stigma, Pollination mechanism, Evolution

GUO You-Hao, HUANG Shuang-Quan. Evolution of pollination system and characters of stigmas in Najadales[J]. .

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Evolution of pollination system and characters of stigmas in Najadales

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