Seed micromorphology and its systematic significance in tribe Alsineae (Caryophyllaceae)

- Seed morphology provides valuable data in delimitation of taxa in Cerastium-Stellaria complex.
- Six types of seed surface are defined among the studied taxa.
- Size, shape and number of seeds per capsule are most important macromorphological characters.
- Seed features support dividing both Cerastium and Stellaria in two different groups

Despite the increasing number of molecular phylogenetic studies conducted recently in Caryophyllaceae, the relationships within several major lineages remain unresolved. Tribe Alsineae including the large genera Cerastium and Stellaria is among the poorly studied taxa in the family in terms of seed morphology. In order to test the utility of seed characters in delimitation of genera in the Stellaria-Cerastium complex, seeds of eight genera and 66 taxa were studied morphologically using light and scanning electron microscopy (SEM). Among the scored characters, seed size and shape provide valuable diagnostic information at generic rank. In addition, six types of seed ornamentation are recognized which might be attributed to different genera of tribe Alsineae. The most remarkable seeds in terms of color and ornamentation were found in members of the genus Dichodon supporting its recognition at the generic rank. Cerastium seeds are characterized mostly by triangular shape, reddish brown color and colliculate, tuberculate, or rugose testa, while Stellaria can be divided into two groups: large and small seeded taxa. Mesostemma and the large-seeded Stellaria taxa resemble each other, both in gross morphology and in seed micromorphology. In addition the small seeded taxa show two distinct types of seed ornamentation: tuberculate or rugose. Seed characters do not completely support the current sectional and subsectional concept in Cerastium, but they appear to be useful to differentiate subsect. Fugacia as well as some closely related species.