The pollen morphology of 19 species in the genera Potamogeton, Zannichellia and Triglochin from China was examined under light and scanning electron microscopes.
1. Pollen characteristics
(1) Potamogeton L. (Plate 1, 2:1-8) Pollen grains spheroidal, subspheroidal, rarely oblate or ovoid, (17-35)24.41×27.76(18-45)μm in size; anaperturate; exine 1-2μm thick, 2-
layered or obscure; crass-reticulate, reticulate or finely-reticulate under LM, distinctly reticulate under SEM; muri uniform or not uniform, smooth or granular, rarely with processes; bacula thicker or thinner at the intersection of muri.
(2) Zannichellia L. (Plate 2:9) Pollen grains spheroidal, ,(20-26)23.1×24.15(21-27) μm in size; anaperturate; exine 1 μm thick, stratification obscure; nearly reticulate under LM,
shallowly reticulate under SEM; luminae shallow, large and irregular, muri very thin and not uniform; bacula absent.
(3) Triglochin L. (Plate 2:10-11) Pollen grains spheroidal or subspheroidal; (20-30)23.65×23.7(20-30) μm in size; anaperturate; exine about 1μm thick, stratification obscure,
finely reticulate under LM, distinctly reticulate under SEM; luminae rather large or minute; muri uniform, with 1-2 lines of granules, bacula present or absent.
2. Pollen types of Potamogeton L.
(1) Thin muri--thick bacula: Potamogeton pectinatus, P. intramongolicus, P. filiformis, P. pamiricus; (2) Uniform muri and bacula: 1) Large pollen subtype: Potamogeton
crespus; 2) Medium-sized pollen subtype: Potamogeton heterophyllus, P. perfoliatus, P. distinctus, P. malaianus; 3) Minute pollen subtype: Potamogeton oxyphyllus, P. obtusifolius, P. lucens, P. cristatus, P. gramineus, P. octandrus, P. pusillus.