The Monkey Pod tree (Albizia saman; Fabaceae - Mimosoideae) is native to the grass savannah of northern South America and is widely cultivated in the tropics as an ornamental and for shade. It has a dense, spreading crown, sometimes 30 m across, with widely spreading branches from low down. Pods are straight, green turning dark brown or black, 12-20 cm long, 1-2 cm wide, 1.2 cm thick, indehiscent, containing numerous seeds embedded in a resinous, sticky, brownish pulp. A mature tree can produce in excess of 1000 pods in a season. The gummy pods stick to shoes and slippers and are not easily swept from sidewalk surfaces.
Sterile, non-seeding forms of these species would be desirable for landscape purposes. Since a triploid (3N) plant, the progeny of a tetraploid (4N) crossed to a diploid (2N) would likely be sterile, procedures were used to first create tetraploid plants by treating meristems of diploid seedlings with 0.1% colchicine solution for 48 h. One tetraploid Delonix and 10 or more tetraploid Albizia trees began flowering at age 6 years and have flowered annually for the past 3 or 4 years. Crosses to the respective diploid forms have not been successful to date, but the induced autotetraploid plants have much reduced fertility and reduced pod production. The 4N Delonix produces about 90% fewer pods than a 2N plant of similar size. The pods usually contain aborted seeds. The occasional seeds that appear normally formed, do not germinate.
The 4N Albizia trees produce a range of abnormal pods, including some as short as 3 cm long and others that don’t produce seeds or resin. Total pod production is reduced, but the degree of reduction has not been determined. The best selections will be grafted for increase and distribution.