Grimes, Mimosoid legumes 
747 
about the polarity of the heterotopic change in stipule inception until a better resolved 
cladogram becomes available, and morphology of the stem-apex of more species is 
studied. Sattler (1978) pointed out that though the position of an organ may be 
evident, the direction of change (i.e., polarity) may not be known, and cautioned 
that one cannot assume that the unusual position is necessarily derived. 
All the species studied possess inflorescences which at anthesis can be described as 
pseudoracemes of capitula, and while the unit-inflorescences are probably 
homologous, the differences found clearly show that the pseudoracemes of capitula 
are not homologous as a type of inflorescence. They differ in heterochronic changes, 
and in hierarchical origin of unit-inflorescences. In Pnraserianthes lophantha and 
PUhecellobium duke the unit-inflorescence forms directly from the apical meristem of 
a primary bud (a bud formed directly in the leaf-axil). Though the meristem is 
covered by a bract, no other bracts form above the inflorescence. In Lysiloma 
microphyllum, in contrast, the inflorescences clearly form axillary to leaf-primordia 
(?bracts) on short-shoots; the primary bud itself is a condensed shoot-system and 
the meristem of the unit-inflorescence forms from a secondary bud. This stage of 
inflorescence-development has not yet been seen in the other species. Few would 
disagree that the unit-inflorescences (capitula or spikes) are homologous between 
the taxa studied here, and indeed probably throughout the subfamily Mimosoideae. 
However, the variation in position of the unit-inflorescences might better be seen as 
a separate character of a different order. 
The major heterochronic difference in terms of origin of inflorescences can be seen 
as a temporal difference in the fate of buds. In Ebenopsis ebano all inflorescences arise 
on short-shoots axillary to a leaf, which develops more slowly. All nodes formed on 
the short-shoot apparently form unit-inflorescences. In P. lophantha, A. nilofica, 
P. duke and Z. tetragona the unit-inflorescences develop sylleptically from axillary 
buds, but there is temporal differentiation of the buds: only those buds formed at 
the end of the formation of the RGU develop into unit-inflorescences. 
Lysiloma microphyllum and Pifhecellobium duke are unusual in that there is simultaneous 
blooming of unit-inflorescences that have developed both proleptically and 
sylleptically on axillary buds; the proleptic ones from a previous RGU, the sylleptic 
ones form a current RGU. Following the definition of inflorescence presented by 
Grimes (1992) the inflorescence of these species is not the totality of unit-inflorescences 
produced along a stem made up of many RGUs, but rather the series of one or few 
floriferous nodes of the short-shoots. 
Acknowledgements 
This research was supported by the Harding Laboratory of the New York Botanical 
Garden. The generosity of the Director, Dr. D.W. Stevenson is gratefully acknowledged. 
1 wish to thank the following staff of the Propagation Range of the New York Botanical 
Garden for access to the collections, and for adopting some of my orphaned specimens: 
Len Marino, Mobee Weinstein, Greg Pietrowski, Francisca Coelho, Sharita Mason 
and James Harkins. 
References 
Briggs, B.G. & Johnson, L.A.S. (1979) Evolution in the Myrtaceae — Evidence from inflorescence 
structure. Proc. Linn. Soc. Nezv South Wales 102: 157-256. 
Brown, C.L. & Sommer, H.E. (1992) Shoot growth and histogenesis of trees possessing diverse 
patterns of shoot development. Aiiier. J. Bot. 79: 335-346. 
