The flowering and fruiting phenology and breeding system of Cistus alb
idus L. are studied. Four phases are established for the development o
f the flower, which remains open for a period of less than 14 hrs, alt
hough this time-span can be further reduced if environmental condition
s are unfavourable. Only 65.6% flowers develop ripe fruits, the greate
st losses occurring in the change from flower to unripe fruit. it is a
xenogamous species with a P/O ratio of 5.426 +/- 816. Experimentally,
fruits may be formed by autogamy through manual pollination, although
this does not occur spontaneously. There is recognition by the plant
of its own pollen tube, which reduced the production of fruits by auto
gamy. This mechanism can be considered as cryptic self-incompatibility
system.