Orlovich, Drinnan & Ladiges, Floral development in the Metrosideros group 
713 
have reached a considerable size and gynoecium formation is well underway. The 
pre-staminal bulge that has developed in front of each petal is well formed, and has 
two recognisable halves separated by a vertical groove. It was not possible to 
determine unequivocally the exact relationship between the petal primordium in the 
strict sense and the pre-staminal bulge, but we interpret them here as independent 
structures. Because of the invaginated nature of the floral apex the pre-staminal 
bulge gives the appearance of having formed on the base of the developing petal 
primordium. However, this region of the cone is actually the flank of the floral apex 
immediately acropetal to the petal primordia, and it is more likely that the pre- 
staminal bulge forms on the floral apex proper. Species of Eucalyptus informal 
subgenus Eudesmia also have stamens that form on an antepetalous buttress. However, 
these buttresses were interpreted as modified corolline components that are 
homologous to the petals of Angophora and the bloodwood eucalypts (Corymbia) 
(Drinnan & Ladiges 1988, \989a,h). They are not equivalent to pre-staminal bulges in 
Lophostemon, Welcliiodeiidron and Tristaniopsis. 
Fig. 21. Floral development of Tlinlcropin cpicenslandica. a, part of a flower hud with two petal 
(P) and four stamen (S) primordia. There is a difference in size between adjacent petals. The 
stamen primordia are initiated directly on the wall of the hypanthium, not on a swollen PSB 
(x 250); b, petal and stamen primordia. The older stamens are initiated opposite the petals. 
The younger stamen is lower down on the hypanthium and is antesepalous (x 250); c, part of 
a flower bud illustrating the tight packing of the stamen primordia. The outermost stamen 
primordia (left and right) are antesepalous and are smaller than the antepetalous stamens in 
the centre (x 285); d, mature flower bud with five sepals (K) and six petals (P) removed. There 
is one free stamen (S) in front of each petal and another stamen (S*) inserted in an irregular 
position (x 90). (from DAO 199). 
