Aims Flower syndrome and pollination characteristics are the basis and main driving forces of the evolutionary success of flowering plants. Lycium ruthenicum is a national second-class protected plant distributed in northwest China, with two flower morphs, i.e. homostylous flower (style length is similar to stamen length) and flower with approach herkogamy (style length is longer than stamen length). However, little is known about the flower syndrome and pollination characteristics of the different flower types of L. ruthenicum.
Methods In this study, we compared the flowering phenology, flower characteristics, flower reward, and pollination characteristics of two different flower morphs of L. ruthenicum.
Important findings In Kashi natural populations, there is no significant difference in the height of sexual organs of homostylous flower, but it is significant in the herkogamous flowers. The corolla diameter, corolla tube length, number of ovules of homostylous flowers are higher than that of herkogamous flowers. The stamen-stigma distance, number of pollen and pollen/ovule (P/O) of herkogamous flowers are higher than that of homostylous flower. The proportion of homostylous individuals (68%) is higher than that of herkogamous (32%). Population and individual level flowering times were significantly different between the flower morphs and were longer for homostylous flower individuals ((117.00 ± 2.25) d, (101.65 ± 1.98) d) than that of herkogamous flower individuals ((26.00 ± 1.00) d, (18.75 ± 1.00) d), but the longevity of herkogamy flowers ((4.50 ± 0.14) d) are longer than that of homostylous flowers ((3.13 ± 0.11) d). At early flower stage (purple phase) the nectar volume of two morphs is significantly higher than late stage (white phase). In the purple phase the main pollinators were Bombussp., Apis mellifera and Syrphidae, and the visiting frequency and duration of stay on the homostylous flowers are higher than that of herkogamy flowers. In the white phase, the main pollinators on the herkogamous flower have higher visiting frequency than that of homostylous flower. At the different phases the number of pollen deposited on the stigma, pollen removal rate, pollination efficiency of homostylous flowers are higher than that of herkogamous flowers. The fruit and seed set of homostylous flowers are higher than that of herkogamous flowers. Under the extreme environment of sandstorms in southern Xinjiang, homostylous flowers can secure reproduction through high self-compatibility, and herkogamous flowers will increase outcrossing rate in the population. These differences in flower traits and pollination adaptations may be the main factor affecting the reproductive success of L. ruthenicum.