Leaf Forms in Macadamia

W. B. Storey*

Until L. S. Smith of the Botanic Museum and Herbarium at Brisbane, Queensland, Australia revised the species of the cultivated macadamias and identified each species with its valid botanical name in 1956 (8), the names of the three species principally concerned were thoroughly confused. The confusion becomes immediately apparent to anyone delving into the early history of the Macadamia as a cultivated crop. In 1959, I published two articles in the California Macadamia Society Yearbook, one enumerating the species in the genus Macadamia (9), the other reviewing the history of the systematic botany of the Australian species (10). These articles attempted to inform the reader on the present understanding of the genus and to tell how the state of utter confusion came about. To recapitulate briefly with regard to the three species involved, I offer the following:

M. ternifolia. This species is the one commonly known as "Maroochy Nut" or "Gympie Nut." It was the first Macadamia t o be discovered botanically. It was discovered in 1857 by the botanists Ferdinand Von Mueller and Walter Hill. Mueller established the name of the genus and described the first species (7). It soon lost its identity, however, for, in 1860, Mueller, himself, gave it a new name, this time Helecia ternifolia. In 1910 and 1911, the Australian botanist F. M. Bailey, believing he had discovered two new species, gave his type specimens the names M. minor and M. low ii, respectively (1, 2). In 1954, L. A. S. Johnson of the National Herbarium of New South Wales assigned the name to the species now known as M. integrifolia (4). It was not until 1956 that Smith (8) determined conclusively that M. ternifolia, M. minor and M. lowii were different names for the same species, with M. ternifolia having priority.

M. tetraphylla. This species is the one commonly known as the "roughshell Macadamia." The exact date of its discovery is unknown. The earliest description is that by Bentham in 1870 in his Flora Australiensis under the name M. ternifolia, based on herbarium material under that name in the herbarium at Melbourne (3). It masqueraded under that name until 1954, when L. A. S. Johnson determined it to be a species which had never been properly named, although it had been known botanically for 84 years and its cultivation had begun by 1893 (11), if not earlier. He named it M. tetraphylla (4).

M. integrifolia. This species is commonly known as the "smooth-shell Macadamia." J. H. Maiden and E. Betche of the Botanic Garden at Sydney (5) described it botanically in 1897, although the species itself is native to Queensland. They named it M. integrifolia originally, but, in 1899, they decided it was just an extreme variation of what was then thought to be M. ternifolia (today’s M. tetraphylla) (6), and changed the name to M. ternifolia bot. var. integrifolia. It was brought into cultivation under this name, which pcrsistcd until 1954, when Johnson decided that this species must he the real M. ternifolia (4). Final clarification came from Smith in 1956 (8), who restored to the species the name M. integrifolia that had been bestowed upon it in the beginning by Maiden and Betche.

Much of the confusion that has existed with respect to proper identification and typification of Macadamia species is due to unsettled growth habits and environmentally induced variations in the species.

Examination of young seedlings reveals that, in juvenile characters, the three species are remarkably alike. As the seedlings grow, specific differences become more distinctive, but, not until the trees are two or more years old, do they begin to discard most of their juvenile characters. New branches, which arise near the ground and sucker shoots from old trees, may show juvenile characters at first appearance.

All species fluctuate in numbers of the leaves at the nodes. Nodes with two, three, four, and five leaves can be found in all species, although the basic number of M. ternifolia is considered to be three, of M. integrifolia to be three, and of M. tetraphylla to be four.

The margins of the blades of juvenile leaves of all three species are finely to coarsely toothed. Generally, the points of the teeth end in fine fairly stiff spines. As the trees mature the numbers of teeth may become less. Leaves from adult branches of M. tetraphylla may have anywhere from 10-35 on a side. Those of M. ternifolia usually have 8-12, while those of M. integrifolia may have 1-5, or may lack them entirely.

Figure 1 shows a short piece of stem from M. ternifolia showing four nodes. There are three leaves in a whorl at the lowest node. The next node above has four leaves, and the one above that has five leaves. The uppermost node is back to four.

Figure 3 shows four leaves from M. ternifolia. The leaf at the left is from a 2-year-old seedling. The other three are from a grafted tree, the scion of which was collected from a very old tree in Australia. As indicated in the photograph, juvenile leaves from seedling trees tend to be larger than those from adult trees, and to have 10-20 teeth on a side. The leaves of adult trees are smaller and less toothed for the most part, but as shown in a typical leaf on the right, some teeth arc always present. Also, all leaves have distinct petioles, i.e. leaf stalks.

Figure 4 is a photograph of leaves of M. tetraphylla, with a juvenile leaf on the left and the least serrated adult leaf that could he found on the right. The transition from numerous teeth to relatively few is evident, but, in this species, also, some teeth are always present. Juvenile leaves tend to be long and narrow. Adult leaves generally are much longer, but also are proportionately much wider. The leaves of young seedlings may have a short petiole or may he completely sessile, i.e. lacking a petiole. Adult leaves typically are sessile.

Figure 5 shows the leaves of M. integrifolia with the juvenile condition on the left and the completely toothless condition on the right. The leaves of young seedlings tend to be much longer and narrower than those of older trees. All leaves typically are petiole.