The unit inflorescence (the umbel) is made up of apparently predetermined numbers of buds on the peduncle (e.g. 1, 3, 7, 9 11, 13 etc.). Accurate determination of bud number is very helpful in identification. Note that during bud development one or more buds may abort, leaving a scar which can usually be seen on the summit of the peduncle, so the real bud number can be worked out.
Bud number per umbel will be one (or more) of the following states:
One-flowered
There is a single bud at the summit of the peduncle (e.g. Eucalyptus globulus subsp. globulus, E. verrucata).
Three-flowered
Three buds form at the summit of the peduncle. They occur in a line at right angles to the stem (e.g. E. viminalis, E. erythrocorys, E. tetrodonta).
Seven-flowered
Seven buds form at the summit of the peduncle (e.g. E. mannifera, E. miniata). The "basic three" can usually be seen at right angles to the stem with four more placed symmetrically between them but slightly displaced or, if the buds are clearly stalked, six buds will appear around a central bud which often has a slightly longer stalk.
More than seven up to fifteen-flowered
The buds may be seen in nines or elevens, again in recognizable symmetry (e.g. E. pauciflora), or in even greater numbers when the symmetry is largely lost (eg. E. andrewsii, E. jucunda).
More than fifteen-flowered
Each unit inflorescence has more than fifteen buds (e.g. E. mcquoidii, E. phoenicea). E. macrandra can have more than 50 buds umbel while E. elata often has more than 30.
