The relation between stigma position and receptivity in two flexistylous gingers
两种姜科花柱卷曲性植物柱头的位置与其可授性的关系

Flexistyly is a unique sexual dimorphic system found in Amomum and Alpinia species of the gin-ger family (Zingiberaceae). The populations of flexistylous species have two phenotypes, named an anaflex-istylous morph and a cataflexistylous morph, and all individuals of both morphs separate their male and fe-male functions spatio-temporally. We conducted manipulated pollinations and pollen tube growth experi-ments on Alpinia blepharocalyx and A. galanga to detect the manner of separation of male and female func-tions within the individual and its adaptive significance. The results showed that the outcrossing rates of ma-nipulated and natural pollination in the cata-morph did not differ significantly (P>0.05). However, the num-ber of seeds per fruit of manipulated cata-morphs was significantly lower (P<0.01) than that of control indi-viduals, perhaps due to the inbreeding depression caused by ovule discounting. Pollen tube growth experi-ments showed that, when stigma were located at the receptive position (ana-morph in AM, cata-morph in PM), stigma provided appropriate conditions (had stigmatic secretion) for pollen grain germination, and pol-len tubes penetrated into the style within 2 hours after pollination, regardless treatment of selfing or out-crossing. However, when stigma were beyond the anther (ana-morph in PM, cata-morph in AM, without stigmatic secretion), it usually took 6-10 hours for pollen germination and pollen tube penetration. Pollen tubes, however, could reach the ovary within 24 hours under both treatments. Hand-pollination also showed that pollen grains of anaflexistylous flowers have matured before the dehiscence of pollen sacs. Our research suggests that flexistyly is a floral dimorphism comprising reciprocal mobile herkogamy and heterodichog-amy. Heterodichogamy encourages outcrossing, meanwhile reciprocal curvatures of stigmas play a role of reducing interference between male and female functions.