Populations of Thismia tentaculata （Burmanniaceae tribe Thismieae） are described and illustrated from Tai Mo Shan in Hong Kong, southern China. This represents the first report of the genus and tribe from continenta...Populations of Thismia tentaculata （Burmanniaceae tribe Thismieae） are described and illustrated from Tai Mo Shan in Hong Kong, southern China. This represents the first report of the genus and tribe from continental China.展开更多
Although ＂dry-type＂ stigmas are widely re- garded as ancestral in angiosperms, the early-divergent family Annonaceae has copious stigmatic exudate. We evaluate three putative functions for this exudate： as a nutrit...Although ＂dry-type＂ stigmas are widely re- garded as ancestral in angiosperms, the early-divergent family Annonaceae has copious stigmatic exudate. We evaluate three putative functions for this exudate： as a nutritive reward for pollinators; as a pollen germination medium; and as an extragynoecial compitum that enables pollen tube growth between carpels. Stigmatic exudate is fructose dominated （72.2%）, but with high levels of glucose and sucrose; the dominance of hexose sugars and the diversity of amino acids observed, including many that are essential for insects, support a nutritive role for pollinators. Sugar concentration in pre-receptive flowers is high （28.2%）, falling during the peak period of stigmatic receptivity （17.4%）, and then rising again toward the end of the pistillate phase （32.9%）. Pollen germination was highest in sugar concentrations 〈2%. Sugar concentrations during the peak pistillate phase therefore provide optimal osmolarity for pollen hydration and germination; subsequent changes in sugar concentration during anthesis reinforce protogyny （in which carpels mature before stamens）, enabling the retention of concentrated exudate into the staminate phase as a pollinator food reward without the possibility of pollen germination. Intercarpellary growth of pollen tubes was confirmed： the exudate therefore also functions as a suprastylar extragynoecial compitum, overcoming the limitations of apocarpy.展开更多
文摘Populations of Thismia tentaculata （Burmanniaceae tribe Thismieae） are described and illustrated from Tai Mo Shan in Hong Kong, southern China. This represents the first report of the genus and tribe from continental China.
基金funded by grants from the Hong Kong Research Grants Council(776713)the University of Hong Kong Research Committee,both awarded to R.M.K.S.and C.C.P.
文摘Although ＂dry-type＂ stigmas are widely re- garded as ancestral in angiosperms, the early-divergent family Annonaceae has copious stigmatic exudate. We evaluate three putative functions for this exudate： as a nutritive reward for pollinators; as a pollen germination medium; and as an extragynoecial compitum that enables pollen tube growth between carpels. Stigmatic exudate is fructose dominated （72.2%）, but with high levels of glucose and sucrose; the dominance of hexose sugars and the diversity of amino acids observed, including many that are essential for insects, support a nutritive role for pollinators. Sugar concentration in pre-receptive flowers is high （28.2%）, falling during the peak period of stigmatic receptivity （17.4%）, and then rising again toward the end of the pistillate phase （32.9%）. Pollen germination was highest in sugar concentrations 〈2%. Sugar concentrations during the peak pistillate phase therefore provide optimal osmolarity for pollen hydration and germination; subsequent changes in sugar concentration during anthesis reinforce protogyny （in which carpels mature before stamens）, enabling the retention of concentrated exudate into the staminate phase as a pollinator food reward without the possibility of pollen germination. Intercarpellary growth of pollen tubes was confirmed： the exudate therefore also functions as a suprastylar extragynoecial compitum, overcoming the limitations of apocarpy.
