Pollen grains of the seed plant genera
Ephedra L. and Welwitschia
Hook. f. (Gnetales) are of similar
size, shape, and have a polyplicate exine with alternating thicker and thinner regions.
considered inaperturate and the exine is shed during germination, leaving the male gametophyte naked.
The shed exine curls up and forms a characteristic structure with transverse striations. Such upcurled
exines have been found in situ in Early Cretaceous seeds with affinities to
. The purpose of this
study was to document the germination of
pollen and investigate whether they also discard
their exine during this process.
The pollen grains of
are monoaperturate with a distinct, distal sulcus. During
germination, the sulcus splits open and the gametophyte expands to a spherical form that extends out
of the exine. The pollen tube starts to grow one or two hours later and as in
, it is displaced
towards one side. The exine is not shed but remains as a ‘‘cap’’ that partly covers the male
gametophyte. Thus, in this respect the germination process is distinctly different from that in
and this study demonstrates that discharging the exine during pollen germination is unique to
among the polyplicate pollen producing genera in the Gnetales.
Taylor & Francis , 2005. Vol. 44, no 3, 137-141 p.