Minor differences with big consequences: Reproductive patterns in the genus Gagea (Liliaceae)

Reproductive patterns in ten species of Gagea Salisb. were compared by counts and measurements of bulbs, bulbils and flowers in large cohorts including all life stages. Two types of bulbils were found: taxa with “type I bulbils” start to develop a single to several bulbils as soon as the replacement bulb has reached a certain diameter and then continue to form them indefinitely throughout the life of the plant. “Type II bulbils” are only temporarily produced in immature, non-flowering plants of some species, but not in fully grown, flowering individuals, a phenomenon termed “reproductive switch”. Patterns of bulbil formation are species-specific: G. davlianidzeae, G. nigra, G. peduncularis, G. pratensis, and G. spathacea produce only type I bulbils; G. angelae, G. fedschenkoana and G. lutea develop only type II bulbils. Both bulbil types occur simultaneously in G. fragifera and G. villosa. The quantitative investigations demonstrate the existence of species-specific thresholds for the development of bulbils as well as flowers. Compared to the adult volume of the replacement bulb (where 90% of all plants flower), both types of bulbils have usually low thresholds: 0–5% (type I, all but one species) and 3–13% (type II). Inflorescences develop if plants attain between 38 and 60% of the adult bulb volume. Minor changes in patterns of bulbil formation and thresholds for their development may ensure survival of highly sterile taxa (e.g. G. spathacea, G. fragifera). This, in turn, can facilitate speciation in the genus driven by both hybridization and polyploidization.