Systematic embryology of the Scilla siberica alliance (Hyacinthaceae)

Eleven species of the Scilla siberica alliance, a well defined monophyletic group within the "genus by tradition" Scilla , have been investigated embryologically with special reference to embryo sac and endosperm development. Data are now available for 15 out of 20 known species. In most species embryo sacs develop according to the bisporic Allium-type, only in Scilla rosenii according to the tetrasporic Drusa-type. Endosperm development is either nuclear or helobial (in 10 and 4 species respectively, unknown in 1). The taxonomic significance of these traits is evaluated after character polarisation by out-group comparison. Among the out-group taxa, S. persica may be considered as the sister group of the S. siberica alliance because only these two groups have an Allium-type embryo sac, a synapomorphy derived from the plesiomorphic Polygonurn-type. The Drusa-type in S. rosenii is an autapomorphy for that species and evolved from an Allium-type embryo sac. S. rosenii is distinct from its sister species S. koenigii , previously thought to be conspecific. Nuclear endosperm is considered to be plesiomorphic rather than apomorphic within the S. siberica alliance, with respect to its occurrence in the presumed sister group and other outgroup taxa (S. hohenackeri group, S. bifolia alliance), but some doubt remains because of a helobial endosperm occurring in the out-group taxon S. messeniaca . The distribution of other synapomorphies within the S. siberica alliance suggests that a helobial endosperm evolved as a synapomorphy for S. bithynica, S. melaina and S. mischtschenkoana , but as a parallel trait in S. leepii . Species status for S. leepii is supported.