M. Suarezcervera et al., STRUCTURE OF THE APERTURAL SPORODERM OF POLLEN GRAINS IN EUPHORBIA AND CHAMAESYCE (EUPHORBIACEAE), Plant systematics and evolution, 197(1-4), 1995, pp. 111-122
The tricolporate pollen grains of 38 Mediterranean and Macaronesian sp
ecies of Euphorbia L. and Chamaesyce S. F. GRAY have a special apertur
al sporoderm not found in the other taxa of the Euphorbiaceae. At the
apertural margo the ectexine is thinner because of shorter columellae
and the thin, fragmented or even absent foot-layer. Ectexinous granule
s, mixed with endexinous material, are present near the era. The endex
ine is homogeneous and thickened under the colpi (at the end and at th
e proximity of the end of colpus). Around the era, the endexine is gra
nulate and lamellar with irregular cavities. The apertural intine pres
ents a characteristic structure with thickenings running along both si
des of the colpi. The arrangement and structure of these intinous thic
kenings depend on the distance from the era. This special morphology o
f the intine is present in all taxa studied here. The genus Euphorbia
is considered to be the most evolved taxon of this family. The charact
eristic apertural sporoderm may be an adaptative modification to diffe
rent physiological conditions, so it may present an apertural mechanis
m which is more adapted to harmomegathic changes and thus facilitate t
he germination and the formation of the pollen tube.