The floral development and floral anatomy of Chrysosplenium alternifolium,an unusual member of the Saxifragaceae

The floral development and anatomy of Chrysosplenium alternifolium were stu died with the scanning electron microscope and light microscope to understa nd the initiation sequence of the floral organs and the morphology of the f lower, and to find suitable floral characters to interpret the systematic p osition of the genus within the Saxifragaceae. The tetramerous flower shows a highly variable initiation sequence. The median sepals and first stamens arise in a paired sequence resembling a dimerous arrangement, but the firs t sepal and stamen arise on the side opposite to the bract Transversal sepa ls and stamens emerge sequentially, as one side often precedes the other; s epals and stamens occasionally arise on common primordia. initiation of the gynoecium is more constant with two median carpel primordia arising on a s unken floral apex. Several flowers were found to be pentamerous with a 2/5 initiation sequence. Flowers were invariably found to be apetalous without traces of petals in primordial stages; this condition is interpreted as an apomorphy. it is postulated that the development of a broad gynoecial necta ry is responsible for the occurrence of an obdiplostemonous androecium. The gynoecium shows a number of anatomical particularities not observed in oth er Saxifragaceae. The presence and distribution of colleters is discussed.