Floral ontogeny and morphology in Gillenia ("Spiraeoideae'') and subfamily maloideae C. Weber (Rosaceae)

A comparison of floral development in Gillenia ( Rosaceae subfamily "Spiraeoideae") with that in seven genera in subfamily Maloideae was undertaken to ascertain similarities between Maloideae and Gillenia floral development, as well as to ascertain the developmental basis for variation in mature Maloideae floral morphology. The analysis also sought information regarding the initiation and development of the syncarpous hypanthial ovary that is encountered in the majority of Maloideae taxa. While most taxa in this study initiated 20 stamens in three pentamerous whorls, flowers of Chaenomeles and Mespilus each initiated more than three whorls of stamens. Development of the gynoecium in all taxa was preceded by a ring primordium in the Maloideae and a flat-topped primordium in Gillenia. Individual gynoecial units formed on these primordia and in all taxa except Cotoneaster remained connate throughout development. Except in Gillenia, intercalary growth beneath the common insertion point of the gynoecial primordia and adjacent hypanthium is responsible for adnation of the ovary wall and hypanthium observed in mature flowers. Ovule initiation and development for most taxa, including Gillenia, results in a pair of collateral, anatropous, and apitropic ovules, each associated with a funicular obturator. Two ovules were also initiated collaterally in Mespilus and Crataegus, but in these genera they subsequently become superposed. Multiple ovule primordia are initiated in Chaenomeles and Sorbus, but only Chaenomeles had more than two ovules at maturity. The results of this study are discussed in terms of previous studies of floral development in the Rosaceae and previous hypotheses regarding the origin of subfamily Maloideae from a Gillenia ancestor.