Orlovkh, Drinnan & Ladiges, Floral development in the Metrosideros group 
691 
Materials and Methods 
The eleven taxa studied are listed in Table 1. Fresh specimens were fixed in either 
formalin-acetic acid-alcohol (FAA) or 70% ethanol. For scanning electron microscopy, 
flower buds were dehydrated in 100% ethanol and stained with 0.5% acid fuschin in 
95% ethanol for a minimum of 24 hours to aid visibility during dissection. Buds 
were dissected in 100% ethanol and critical point dried. Mounted specimens were 
coated with gold and examined with a scanning electron microscope (JEOL JSM 
840). Buds fixed in FAA or 70% ethanol were prepared for light microscopy by 
dehydration in ethanol followed by embedding in resin (LR White, London Resin 
Co.). Sections 1.0 pm thick were stained with 0.5% toluidine blue O in 0.1% NajCOj 
(O'Brien and McCully 1981). Flowers were cleared in 10 or 15% NaOH-basic fuschin 
as described in O'Brien and McCully (1981). 
Results 
Lophostemon confertus (R. Br.) Peter G. Wilson & ].T. Waterhouse 
Mature flowers of L. confertus have five sepals, five petals and five antepetalous stamen 
fascicles with approximately 70 filaments each (Fig. 1). The first two sepal primordia are 
initiated asynchronously in a decussate position relative to the bud scales (Fig. 2a). 
Subsequent sepals are initiated in a spiral pattern. The floral apex invaginates and the 
petal primordia are initiated on the flank of the developing concave floral apex (Fig. 2b), 
continuing the spiral pattern initiated in the sepals. Following petal initiation, a pre- 
staminal bulge (PSB) develops in the region centripetal to each petal primordium (Fig. 
2c, 3a) and a shallow vertical, groove-like depression develops in each bulge (Fig. 2d). 
Each antepetalous PSB remains distinct from those adjacent to it, which are different 
sizes due to asynchronous initiation (Fig. 2e). Stamens form on the PSB. The initiation of 
stamen primordia is bilaterally symmetrical around the shallow depression (Fig. 2f). The 
first-formed stamens are initiated in the centre of the PSB and along its top edge; 
subsequent stamens are initiated along both sides of the PSB (Fig. 2g) and always on the 
adaxial surface. The depression forms a notch in the top of the fascicle (Fig. 2h) and 
continues along its abaxial side (Fig. 2i). As the flower bud develops, the abaxial side of 
each PSB elongates to form a staminal fascicle that is bifid (Fig. 3b-^). Free stamens arise 
only from the adaxial side of the fascicle. The oldest stamens are those situated along the 
axial midline of the fascicle and younger stamens are positioned along the edges. Vascular 
traces of individual stamens remain distinct for the full length of the fascicle (Fig. 3e). 
Lophostemon suaveolens (Soland. ex Gaertn.) Peter G. Wilson & j.T. Waterhouse 
Mature flowers of L. suaveolens (Fig. 4a) have five sepals, five petals and five 
antepetalous stamen fascicles. The fascicles, like those of L. confertus, are bifid 
(Fig. 4b). The first two sepals are initiated asynchronously in a position decussate to 
the two floral bracts (Fig. 5a). A third sepal is initiated in space on the enlarging 
floral apex (Fig. 5b). At about the same time as the initiation of the third sepal, the 
floral apex invaginates (Fig. 5c). Subsequent sepals are initiated in a spiral sequence 
(Fig. 5d). The first petal primordium is initiated in the same sequence as the sepals 
(Fig. 5d) and is followed by the asynchronous initiation of the remaining four 
(Fig. 5e). As the petal primordia develop, the region directly centripetal to each petal 
primordium enlarges, forming a pre-staminal bulge (PSB) (Fig. 5f). The PSBs develop 
asynchronously (Fig. 5g) corresponding to the size of the associated petal. A vertical 
groove develops in each PSB (Fig. 5h) and stamen primordia are initiated 
symmetrically around this groove (Fig. 5i). Stamens are first initiated along the top 
