Floral organ sequences in Apiales (Apiaceae, Araliaceae, Pittosporaceae)

Abstract

It is remarkable that families like Apiaceae and Brassicaceae, characterised by uniform floral diagrams (i.e. stable positioning of floral organs relative to one another), show a great variability in initiation sequence of the floral organs. Within the subfamily Saniculoideae of the Apiaceae temporal overlaps in the initiation of the floral whorls ( Astrantia ), the formation of common stamen-sepal primordia ( Astrantia ), and segmentation in the formation of petals in pairs ( Sanicula ) occur. Reduction of the calyx and shortening of the plastochrons toward zero are trends found in the more advanced Apioideae ( Foeniculum , Levisticum ). Hydrocotyle , with its early sympetaly, resembles the Araliaceae more closely. Of interest is the fact that in Araliaceae the flower orientation is variable. Sometimes one sepal is opposite the subtending bract, a feature which becomes fixed in Cyphiaceae and Lobeliaceae of Campanulales, a sister group of Apiales.