Orlovich, Drinnan & Ladiges, Floral development in the Metrosideros group 
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expanding hypanthial region between the developing corolla and gynoecium. Much 
has been written on the nature of the hypanthium and the problems of terminology in 
flowers with deeply concave floral apices, and we do not intend to enter that controversy 
in any substantial way. We consider the inclined walls of the sunken floral apex 
equivalent to the flank of the apical dome of a normal, convex, floral meristem, and 
the resultant hypanthium to be either basically axial or de novo, but not in any way 
equivalent to, or modified from, the bases of the floral organs. 
The spiral phyllotaxy of the corolla is an important determinant of flower form. 
Because petal primordia are sequentially initiated, they are all at different stages of 
development at any one time. The positions of the petal primordia influence the 
sites available for stamen initiation, so the degree to which petal initiation and 
development is asynchronous determines variation similarly in the androecium. 
Fig. 17. Metrosideros collina van villosa. Mature half flower (x 7.9). (from DAO 44). 
