雪莲(Saussurea involucrata)是一种典型的高山草本植物, 同时也是我国重点保护的珍稀药用植物。该文对雪莲的开花生物学特性及其对高山环境的适应策略进行了观测与分析。主要结果如下: 雪莲不育花序单生于茎生叶的叶腋内, 可育复头状花序生长于茎顶端, 由26 ± 7个头状花序构成, 每个花序的小花数为137 ± 34个。复头状花序外侧为绿色至淡黄色半透明的茎生苞叶所包被, 开花过程中, 白天茎生苞叶内侧温度和湿度明显高于外侧的温度和湿度, 最大温差达7.2 ℃, 最大相对湿度差达54.2%, 可为苞叶内侧花序中小花的传粉和受精以及胚和种子的发育提供良好的微环境。不同年份间雪莲的开花物候差异不显著(p > 0.05), 群体花期为65-75天, 单株花期为45-55天, 盛花期持续时间约35天, 平均每株每天开花数为201个, 属于集中开花模式, 有利于吸引传粉者。单花开放持续时间为4-6天, 小花泌蜜持续时间为3天, 其泌蜜量与糖浓度于每天 12:00时达到最高值, 但随着开花的持续, 日泌蜜量逐渐增加, 而糖浓度逐渐减少。雪莲花期浓郁的气味、聚合成复头状的可育花序及其紫色小花与充足的泌蜜量, 增加了对传粉者的吸引力。雪莲开花过程中存在的雌雄异位、雄性先熟以及被动式花粉次级展现现象, 减少了自花授粉的可能性。自然条件下, 其头状花序的结籽数和结籽率分别为126.0 ± 10.5粒和91.7% ± 4.2%, 单株结籽数为3 326.4 ± 28.7, 表明雪莲在高山极端环境中能顺利地完成有性生殖过程。

Aims Saussurea involucrata is not only a rare and protected species, but also an important traditional Chinese medicinal plant. The species is an herbaceous monocarpic perennial that grows in the alpine zone. Our objective was to investigate floral biology of this species in a high-altitude area of the Tianshan Mountains and to gain an understanding of how its floral biology is adapted to the alpine environment.
Methods The research was conducted at the Tianshan Glaciological Station of the Chinese Academy of Sciences (43°06′ N, 86°49′ E, 3 540 m a.s.l.) in Xinjiang. We selected an undisturbed population of plants and measured and recorded floral characteristics during flower opening. Also, the dynamics of nectar secretion were monitored by collecting nectar with a syringe and determining sugar concentration with a pocket refractometer. Temperature and relative humidity both inside and outside the involucral bracts were measured with a portable hygrothermograph, and number of seeds produced by plants was counted in the field.
Important findings The inflorescence is a compound capitulum composed of many capitula on a short stem, and it is surrounded by large green involucral bracts. About 26 of the uppermost capitula contained 137 ± 34 fertile florets each, but the lower capitula in the axils of the bracts had sterile florets. The maximum temperature and relative humidity differences in one day between inside and outside the bracts were 7.2 °C and 54.2%, respectively. Opening of florets on a single plant lasted about 45-55 days and for the population about 65-75 days. The duration of peak flowering was ca. 35 days, and the mean number of flowering florets per plant each day was 201. Flowering phenology did not differ between years (p > 0.05). Longevity of a floret from open corolla to a wilted stigma was 4-6 days. Herkogamy, protandry and secondary pollen presentation were conspicuous during floret opening, thus avoiding self-pollination and interference between female and male function. Both nectar volume and sugar concentration of a single floret reached a maximum value at 12:00 (solar time) within 1 day. Over a 3-day period of consecutive nectar secretion, nectar volume gradually increased, while sugar concentration decreased. In the natural habitat, mean percent seed set per capitulum and total seed number per plant were 91.7% ± 4.2% and 3 326.4 ± 28.7, respectively. These characteristics are adaptations to the extreme alpine environment of the Tianshan Mountains.