Orobanche hederae Voucher ex Duby (Orobanchaceae) - phenotypic plasticity and seed micromorphology

Orobanche hederae has two colour forms (morphs), normal (euchromatic) and hypochromatic, with numerous intermediary forms: its variability represents therefore phenotypic plasticity rather than polymorphism like in some other species of the genus. Seeds of Orobanche hederae were studied in order to establish whether their micromorphologic characters depend on the climate of the station, on the colour morph of the mother plant or on the year. Two populations were selected: one in Lyons (France), the other in Leuven (Belgium); published data from Sicilia were used for comparison. The studied populations are dominated by hypochromatic forms; euchromatic ones might be more numerous in the Mediterranean region (this result requires confirmation). Characters related to the external form are very variable and thus unfit for systematic purposes; seed ornamentation is identical in all studied plants. No correlation has been detected: either with the locality, the year, or with the colour form of the mother plant. The phenotypic plasticity in Orobanche hederae is therefore comparable to the variability of Platystemon californicus (no correlation between coloration and morphology) rather than to Protect in which a pleiotropic effect on seed size has been observed.