Sexual polymorphisms in Narcissus triandrus (Amaryllidaceae): Is this species tristylous?

The sexual polymorphism tristyly is well documented in three flowering plant families (Lythraceae, Oxalidaceae and Pontederiaceae). Controversy has arisen as to whether the polymorphism exists in Narcissus triandrus L. of the Amaryllidaceae. Surveys of floral variation in 80 populations in Spain and Portugal were undertaken to determine the nature of sexual polymorphisms in the species. Most populations (85 per cent) contained three discrete floral morphs that differ from one another in the sequence in which the stigma and the two anther levels within a flower are presented. Hence, the species is genuinely tristylous. Floral morph frequencies deviated strongly from the isoplethic expectations (1:1:1) typical of tristylous species. Average frequencies for the morphs were L morph = 0.59, M morph =0.19 and S morph = 0.22. In 15 per cent of the populations sampled, the mid-styled morph was absent. Controlled crosses indicated that individuals are moderately self-sterile but cross-compatible with other individuals, regardless of morph. Therefore, the species does not possess a conventional heteromorphic incompatibility system. Self-sterility operates in the ovary, and prior self-pollination of flowers renders ovules nonfunctional as judged by reduced seed-set in subsequent cross-pollinations. Multilocus outcrossing estimates in four tristylous populations averaged t = 0.77, range 0.68-0.87, with significant variation evident among morphs but not populations. All population estimates were less than 1, indicating significant amounts of selfing. Although N. triandrus is clearly tristylous, the expression of the polymorphism is unique among tristylous families.