Orlovich, Drinnan S Ladiges, Floral development in the Metrosideros group 
705 
stamens are initiated in several tiers (Fig. 16b). Expansion of the hypanthium as the 
flower enlarges causes many of the stamens to be spread out on the mature flower 
(Fig. 16c), but failure of the hypanthium to expand in the region directly in front of 
the petals leaves some stamens clustered in those areas (Fig. 16d). There is no fusion 
of filaments within the antesepalous stamen clusters. 
Metrosideros collina (].R. & G. Forst.) Gray var. villosa (L /.) A. Gray 
Mature flowers of M. collina var. villosa have a single row of free stamens around the 
edge of the hypanthium (Fig. 17). Small swellings that may represent pre-staminal 
bulges develop on the hypanthium following initiation of the petal primordia 
(Fig. 18a). Stamens are initiated in a single row on each swelling (Fig. 18b). As the 
bud matures (Fig. 18c, d, e), the filament bases enlarge to fill the circumference of the 
hypanthium. No new stamens are initiated and the small pre-staminal bulges do not 
enlarge. At anthesis, the stamens form a complete ring (Fig. 18f). Occasionally there 
is a gap in an antesepalous region but gaps were not observed in antepetalous 
regions. Occasionally two filaments are fused together (Fig. 18D. 
Tristania neriifolia (Sims) R. Br. 
Mature flowers of Tristania neriifolia have five sepals, five petals and five antepetalous 
groups of stamens arranged in a ring around the hypanthium (Fig. 19). Filaments in 
each stamen group are fused for about half of their length and each group of stamens 
is shortly united at the base. During bud development, a stamen is first initiated 
opposite each petal primordium on the flank of the invaginated floral apex. Two 
further stamens are initiated on either side of the first resulting in a group of three 
stamens opposite each petal (Fig. 20a). Occasionally, one or two extra stamens are 
inserted between the regular antepetalous groups (Fig. 20a). A small degree of 
hypanthial expansion in the antesepalous region accounts for the separation of 
stamens into antepetalous groups (Fig. 20b). 
Thaleropia queenslandica (L.S. Smith) Peter G. Wilson 
The leaves of T. queenslandica are opposite and this pattern is continued in the sepal 
primordia. Two pairs of opposite sepal primordia are present in young buds followed 
by a fifth sepal primordium inserted adjacent to one of the second pair of sepal 
primordia. Five, or occasionally up to seven, petal primordia form more or less alternate 
to the sepals. Tlrey are initiated asynchronously, resulting in petal primordia of differing 
developmental sizes during flower ontogeny. Stamen primordia are inserted around 
the inside of the hypanthium, initially with one stamen more or less in front of each 
petal primordium and several more stamens are initiated in between those first formed 
(Fig. 21a-c). There is variability in perianth and stamen numbers in individual flowers. 
Only the oldest stamens are antepetalous, the younger one or several being lower in 
the concave floral tube and not clearly antepetalous (Fig. 21 d). 
Fig. 13. (left) Floral development of Xanthoslemon oppositifolius. a, petal primordium (P). There are two 
swellings beneath the petal primordium which are stamen primordia (S) (x 240); b, two petal primordia 
(P). Tliere are three stamen primordia visible and one cut away (S) and there is a depression between 
each antepetalous group of stamens (x 300); c, petal primordium and two stamen primordia (x 250); 
d, part of a flower bud showing three stamen (S) primordia in a single row. P - petal (x 150); e, two 
petal primordia and two rows of stamen primordia (x 200); f, stamen primordia. A petal primordium 
has been removed. Stamens are initiated in vertical rows beneath the original antepetalous stamens 
(x 190); g,h, half flower bud showing the vertical rows of stamen primordia (g x 120; h x 100); 
i, flower bud with petals (P) removed. Pairs of stamen primordia are situated on either side of each 
petal scar. Note colleters (C) at the base of the petals (x 90); j, mature flower bud with petals removed. 
Tlie petal bases are swollen and the distance between petals is increased (x 30). (from DAO 221). 
