Floral Ontogeny of Annonaceae: Evidence for High Variability in Floral Form

Annonaceae is a remarkably diverse family of Magnoliales. Dr. XU Fengxia of CAS South China Botanicla Garden and Dr. Ronse De Craene of Royal Botanic Garden Edinburgh, Britain investigated the floral development of 15 species with the scanning electron microscope  to understand the basis for evolutionary change in flowers of Annonaceae. They found that merism is variable with transitions between trimery and tetramery; members of the inner perianth are often in double positions through splitting; stamen and carpel number are variable, although outer stamens are always formed in pairs. They also found an increase of stamen number is correlated with their smaller size at initiation, and limits between stamens and carpels are unclear with easy transitions of one organ type into another in some genera, or the complete replacement of carpels by stamens in unisexual flowers.

The above research results have been published recently by the internationally prestigious journal Annals of Botany.

Flowers at anthesis: (A) Cananga odorata var. fruticosa;  (B) Annona squamosa;
　　　　(C) Mitrephora maingayi;  (D) Desmos chinensis;
　　　　　　　  　(E) Mezzettiopsis creaghii;  (F) Miliusa sinensis (？oral buds).