Orlovich, Drinnan & Ladiges, Floral development in the Metrosideros group 
699 
primordia is clearly evidenced by the different sizes of adjacent primordia early in 
development; (Fig. 9c, d). A pre-staminal bulge (PSB) develops in front of each petal 
primordium. Stamen primordia are initiated on the upper edge of each PSB, which 
develops a distinct notch in its upper edge (Fig. 9e). Stamen primordia develop first 
in the central region of the PSB and then at the edges (Fig. 9f). Stamen bundles 
develop with more or less bilateral symmetry, and there is a clear cleavage between 
each side of each bundle (Fig. 9g). The mature bud contains five bifid antepetalous 
stamen bundles (Fig. 9h). 
Tristaniopsis laurina (Sm.) Peter G. Wilson & J.T. Waterhouse 
Mature flowers of T. laurina have five antepetalous stamen bundles (Fig. 10). Stamens 
are initiated relatively early compared with Lophostemon. Stamens form on pre- 
staminal bulges (PSBs) (Fig. 11a), which form on the flank of the concave floral apex. 
The first stamen primordia are initiated on the upper edge of each PSB (Fig. 11b) and 
subsequently further down as the flower enlarges (Fig. 11c). Expansion of the 
hypanthial rim occurs in the antesepalous regions and stamens are not inserted 
between the initial groups (Fig. lid). Thus the stamens remain in antepetalous bundles 
in the mature flower (Fig. lie). The abaxial side of the PSB does not elongate to the 
Fig. 8. Welchiodendron longivalve. a, mature half flower (x 4); b, stamen fascicle drawn from the 
back (x 6.4). (a from DAO 239; b from Hyland 11042). 
