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Telopea Vol. 6(4): 1996 
Ebenopsis ebano (Berl.) Barneby & Grimes (Figs 6d, 7, 8a-d) 
Ebenopsis is a genus of three species confined to the south-western United States and 
Mexico. The species are all drought-deciduous thorny shrubs with axillary 
brachyblasts. Ebenopsis ebano is common in thickets and subtropical deciduous 
woodlands in north-eastern Mexico (also disjunct in Yucatan) and south-eastern 
Texas. Observations were made on a pair of plants cultivated in the Conservatory of 
the New York Botanical Garden over the course of five years, and a one-time visit 
to a population in Live Oak County, Texas. 
The species exhibits shoot-dimorphism, with long-shoots and short-shoots 
(brachyblasts). All shoots are auxotelic. Phyllotaxy is spiral in a counterclockwise 
direction on both long- and short-shoots (Fig. 8a). The RGU of the long-shoots 
(Fig. 7) is made up of (most commonly) 1-6 metamers each consisting of a primary 
leaf, associated stipular spines, and a sylleptically formed axillary bud. RGUs are 
delimited by a period of dormancy, with no morphological differentiation of the 
dormant branch-apex. The stipules arise independent of but concomitant with the 
leaf-primordium (Fig 8b), but develop much more rapidly. The primary leaf persists 
during the development of several subsequent RGUs, even after the short-shoots 
themselves start to produce leaves. The first axillary bud is visible usually at the 
third plastochron but remains dormant through the seventh (Fig. 8c). Internode 
elongation takes place between the seventh and eighth plastochron, at which time 
the axillary bud develops into a short-shoot (Fig. 8d). 
The RGU of the short-shoot consists of a series of fertile metamers with leaves and 
axillary unit-inflorescences produced in the same phyllotaxy as the long-shoots, but 
the stipular spines of the short-shoots develop neither as quickly nor to such an 
extent as those on the long-shoots. The RGU of the short-shoot differs from that of 
the long-shoot in that the internodes fail to elongate, and all buds axial to 
leaf-primordia form unit-inflorescences. The primordia giving rise to the 
unit-inflorescences develop precociously relative to the subtending leaf, that is there 
is some delayed or perhaps late-suppressed hysteranthy. The inflorescence is a 
pseudoraceme of capitula, but there is only one inflorescence per node. Short-shoots 
uncommonly change into long-shoots, but do so only after several years. Most 
short-shoots continue to produce nodes for a limited number of years: eventually 
they are grown over by secondary growth of the stem. 
Pithecellobium dulce (Roxb.) Bentham (Figs 9, 10a,b) 
Pithecellobium dulce is native from Mexico through Central America south into 
Colombia and Venezuela, but cultivated throughout the world. Observations were 
made over the course of several years on a specimen (since destroyed) cultivated at 
the Conservatory of the New York Botanical Garden. 
Shoots are dimorphic (see below) and growth is apparently anauxotelic, but this 
needs to be confirmed on wild trees as the specimen cultivated at the New York 
Botanical Garden was regularly pruned. The RGU (Fig. 9) consists of a series of 
vegetative metamers (a dozen or so on a healthy branch) consisting of well developed 
leaves, stipular spines, and axillary buds, followed by a series (up to 20 or more on 
healthy branches) of reproductive metamers consisting of nodes with suppressed 
leaves and axillary branches, also with suppressed leaves. Phyllotaxy is spiral 
(Fig. 10a), though in contrast to Ebenopsis ebano and Acacia nilotica the spiral is 
clockwise. Stipules do not arise on the apex, but rather from the flanks of the 
leaf-primordium; they first become visible around the fourth plastochron (Fig. 10a). 
Axillary buds are first visible at the fifth plastochron (Fig. 10a), and are centric 
relative to the subtending leaf-primordium. Subsequently, other buds form lateral to 
the first, and are triserial (Fig. 10c). Internode elongation takes place after the seventh 
