HISTORY OF THE SYSTEMATIC BOTANY OF THE

AUSTRALIAN SPECIES OF MACADAMIA

W. B. Storey *

Reprint from CMS 1959

 In recent years, two Australian botanists, L. A. S. Johnson (15) of the National Herbarium of New South Wales at Sydney, and L. S. Smith (27) of the Botanic Museum and Herbarium at Brisbane, Queensland, have published papers dealing with the systematic botany of Macadamia, particularly as it pertains to the species which are cultivated for their edible nuts. The species diagnoses and nomenclatorial revisions in these papers, although they seem finally to have solved longstanding problems regarding species identification, typification, and delineation, as well as assignment of the valid botanical name to each species, have actually tended to add further to the confusion which already exists in the horticultural literature on the Macadamia.

Most of the articles in the 1958 Yearbook of the California Macadamia Society used the name M. ternifolia in referring to the cultivated smooth-shelled Macadamia. One article (14), however, referred to it as M. integrifolia. In view of the discrepancy, the Editor thought it advisable to insert an Editor’s Note in the Yearbook calling the reader’s attention to the fact that all of the authors were writing about the same species. Furthermore, for the benefit of the layman, as well as the practicing horticulturist who might wish to delve into earlier horticultural literature on the Macadamia, he noted that prior to 1954 M. ternifolia referred to the species now known botanically as M. tetraphylla, between 1954 and 1957 it referred to the species now known botanically as M. integrifolia and from 1957 on, it refers to the species which was formerly known botanically by the synonymous names M. minor and M. lowii. For, in the 100 years which have passed since Mueller (21) established the genus Macadamia and described M. ternifolia as the type species, the name M. ternifolia has been attached to three different species.

The confusion which has existed in the botanical nomenclature of Macadamia has carried over into the realm of horticulture, for the horticulturist, perforce, depends upon the systematic botanist for the correct botanical names of the plants he deals with. There is always a period of transition between the appearance of a revision in the botanical literature and its universal adoption by authors of horticultural papers. The situation in the 1958 Yearbook is a case in point. Consequently, it behooves a person reviewing the literature on the Macadamia to ascertain, if possible, exactly which species or types, as many horticulturists are inclined to call them are being discussed, so that he will not be reading about one species under the impression that he is reading about another.

*Associate Horticulturist, University of California Citrus Experiment Station, Riverside.

In reviewing the botanical literature on the Macadamia I discovered there has long been confusion not only with regard to the true identities of various Macadamia species but also with regard to generic distinctions between Macadamia and a closely allied genus Helicia. For example, one species, which was described originally as H. youngiana, was once transferred to Macadamia and later back to Helicia; three other species which were described originally as H. prealta, H. whelani, and H. heyana are now placed in Macadamia. Even M. ternifolia the type species upon which Mueller (21) founded the genus Macadamia in 1858 was redescribed by Mueller (22) himself in 1860 as H. ternifolia. The differences in interpretations and opinions, which I encountered, led me to trace the history of Macadamia nomenclature through the literature. I set down the results of my library research herein. In so doing I am limiting my remarks to the Australian species, since it is these which have been controversial. A brief report of the genus Macadamia as a whole as interpreted by Sleumer (26) is given in another paper (29).

The botanical history of Macadamia began with the collection of specimens by Walter Hill, Director of the Botanic Gardens at Brisbane, and Ferdinand von Mueller, Royal Botanist at Melbourne, in forests along the Pine River of Moreton Bay, Queensland, Australia in 1857. From these specimens Mueller (21) described M. ternifolia, at the same time establishing the genus Macadamia, which he named in honor of John Macadam, M.D., Secretary of the Philosophical Institute, Victoria, Australia. The descriptions were published in the Transactions of the Philosophical Institute in 1858.

Actually, Fredrich Wilhelm Ludwig Leichardt, a German explorer of Australia during the l840's, collected the first specimen of Macadamia in 1843. Smith (27) says the following with regard to this specimen: "M. ternifolia was first collected by Leichardt at ‘Dullabi, Bunya Bunya Brush’ (Cononondale Ra., S. of Maleny) in 1843. The Stanley River, a tributary of the Brisbane River drains the area, and it is not clear why "Dawson and Burnett Rivers" appears on the label in Mueller’s handwriting. No species of Macadamia have yet been found in either of these river basins. Leichhardt's specimen is at Melbourne." Apparently, Leichhardt's specimen lay in the herbarium as an undescribed species until identified many years later by Mueller after his own discovery and description of the species.

In 1860, Mueller (22) described two new Australian species of Helicia. Helicia is a genus of trees in the family Proteaceae closely allied to Macadamia. It was established by Juan de Loureiro (16) a Portuguese botanist working in Indochina. It consists predominantly of Malaysian species but has a number of Australian representatives. The species described by Mueller were H. glabriflora ("with leaves alternate") and H. ternifolia ("with leaves verticillate-ternate"). Johnson (14), in citing H. ternifolia as a synonym of M. ternifolia states "As published in 1860 it was without any reference to Macadamia ternifolia, and though apparently based on the same material, was described as a new species." Smith (27) also cites H. ternifolia as a synonym of M. ternifolia, and comments as follows, "A. W. Jessup (personal communication) has advised that in the Melbourne Herbarium there are four sheets variously labeled Helicia ternifolia and Macadamia ternifolia in Mueller’s handwriting, and that the specimens were all collected at Pine River, Moreton Bay, by Hill and Mueller in 1857; they comprise the type collection upon which both these names were based. One sheet, now labeled Helicia ternifolia, was obtained on loan, and it shows on the upper right a flowering shoot with a single pseudoterminal raceme from which Mueller’s plate (p.p.m.) of Macadamia ternifolia was probably prepared. This piece is designated LECTOTYPE of the species…". (A lectotype is an additional or associated specimen of the original series from which a species is described which is designated as the type specimen of the species at a date later than the original description.)

In 1862, Mueller (22) described two new species of Helicia, H. prealta and H. ferruginea, both having alternate leaves. In 1870, Bentham (.9) transferred H. prealta to Macadamia.

In 1864, Mueller (22) described another new species of Helicia naming it H. Youngiana C. Moore and F. Muell. This species was later transferred to Macadamia also by Bentham (9).

In 1867, Mueller (22) redescribed H. ternifolia, this time giving M. ternifolia as a synonym and citing his original description of M. ternifolia (21). He also noted affinity to a H. verticillata, which was mentioned by Leichardt. H. verticillata was later transferred to Macadamia by Bentham (9). In a succeeding volume, Mueller (22) referred to H. ternifolia again to note that it had leaves occasionally opposite or in 4’s and 5’s. In 1869, he described the species further, this time under its original name of M. ternifolia.

Bentham (9) in his flora of Australia published in 1870 distinguished between Helicia and Macadamia as follows:

In his discussion under Macadamia he stated, "the genus is endemic in Australia. It is, as observed by Mueller, closely allied to Helicia, but the verticillate leaves, constantly free pedicels, slightly oblique flowers, descending ovules, and more drupaceous fruits may justify the retaining it as distinct." On this basis he recognized three species of Macadamia, M. Youngiana, M. ternifolia, and M. verticillata, and four species of Helicia, H. prealta, H. australasica, H. glabriflora, and H. ferruginea. In his and Hooker’s (10) Genera Plantarum, published in 1880, only M. youngiana and M. ternifolia are recognized. With regard to M. verticillata, they point out that it had been described erroneously as a Macadamia from a cultivated plant in the Botanic Garden at Sydney which proved to be a South African plant Brabeium stellatifolium Linn.

In 1883, Bailey’s (2) synopsis of the Queensland flora was published. Since Bailey continued recognition of M. verticillata it seems probable that he did not see Bentham’s and Hooker’s work, possibly because the two works were in press at the same time, the former in Brisbane and the latter in London. Bailey also recognized M. Youngiana, M. ternifolia, and H. prealta, at the same time noting that in Macadamia the pedicels were free whereas in Helicia they were often connate.

Mueller (23) in a census of Australian plants published in 1889 reduced Macadamia to the solitary species M. ternifolia by restoring M. youngiana to Helicia. Under Helicia he also recognized H. prealta, as well as H. australasica, H. glabriflora, and H. ferruginea.

In 1889, Bailey (3) proposed a new genus, Cyanocarpus, in the Proteaceae closely allied to Macadamia and Helicia, and described C. nortoniana. In the same work he also described a new species of Helicia, H. whelani. I have not seen the publication in which these descriptions appear, so I am uncertain as to whether this description of H. whelani or that which appeared in a third supplement to Bailey’s synopsis (4) constitutes the type description for the species.

A new species of Macadamia was described by Maiden and Betche (18) in 1897, which they named M. integrifolia. Two years later, after examination of herbarium material at Melbourne, the (18) concluded that, because of the great variability and transition between M. ternifolia and M. integrifolia, the latter was only a variety of the former and reduced it to the status of a botanical variety to be known as M. ternifolia var. integrifolia. In a 1904 publication, Maiden (17) described and figured M. ternifolia and the variety integrifolia.

Bailey (5) in his Queensland Flora published in 1901, dissolved the genus Cyanocarpus and transferred the species previously assigned to it to Helicia. At the same time, he transferred H. whelani and H. prealta to Macadamia. The basis for the various changes are found in the following statement: "It is only of quite recent date that the fruits of the Queensland species of Helicia, Macadamia, and Cyanocarpus have become known, and from what I have seen of these have come to the conclusion that it will be better to allow Cyanocarpus to lapse, and arrange the Queensland species thus:

"Those with dehiscent fruits with fleshy or juicy exocarp, and thin or cartilaginous endocarp under Helicia.

"Those with 2-valved or irregularly dehiscent fruits, with more or less coriaceous deciduous exocarp and hard bony endocarp under Macadamia.’

Accordingly, he listed seven species, youngiana, cribbiana, glabiflora, ferruginea, nortoniana, australasica, and heyana under Helicia, and three species, ternifolia, whelani, and prealta under Macadamia.

Two new species were added to Macadamia by Bailey 6, 7) with the publications of type descriptions of M. minor and M. low ii in 1910 and 1911, respectively. These species are mentioned by Bailey (8) in his Comprehensive Catalog of Queensland Plants along with M. ternifolia, M. whelani, and M. prealta (syn. H. prealta). This work seems to have been published in 1912, although the "Prefatory and Other Notes" were written in 1909.

Maiden and Betche (20) in a census of New South Wales plants published in 1916 recognized H. glabriflora, LI. ferruginea and H. youngiana in Helicia, and M. ternifolia, M. ternifolia var. integrifolia, and M. prealta in Macadamia, giving H. prealta as a synonym of the last named species, however.

Francis (13) in 1929 in writing about M. ternifolia stated with regard to the variety integrifolia, "It might be questioned whether it is worthy even of varietal rank, as sharply toothed and quite entire leaves can sometimes be found on the same branchlets." With regard to M minor and M. lowii he commented as follows: "It is not clear to the writer how Macadamia minor and M. lowii differ from each other. Both species could be regarded as small-fruited forms or varieties of M. ternifolia. They also differ to some extent from M. ternifolia in having smaller leaves and unpalatable or perhaps inedible nuts."

When Pope (24) was studying the possibilities of the Macadamia nut as a commercial crop in Hawaii in the 1920’s, he recognized three distinct types as having been introduced from Australia between 1881 and 1894. With regard to the 1881 introduction he states "From Mr. Forbes" description of the tree, however, and particularly from his statement as to the small and undesirable quality of the nuts, the trees are believed to have been of the well-known Gympie nut (Macadamia minor). This opinion is further corroborated by the fact that several Macadamia trees, which produced small, undesirable nuts, grew for some years in Kona, having been brought there as seedlings from the Hamakua district of Hawaii. These trees were recently cut down to prevent the spread of this undesirable variety, which correspond very closely with the description of the Gympie nut given by Rumsey…" (25). I know from personal experience that the principal mark of undesirability was the extremely bitter kernel. The other two types Pope recognized as M. term flora and M. ternifolia var. integrifolia. In describing M. ternifolia he noted that the leaves were oblong-lanceolate, sessile or nearly so, in whorls of 3 or 4, and with serrated and somewhat prickly margins. He described the flowers as creamy white or pink, and the seed surfaces as undulating to bumpy. M. ternifolia var. integrifolia he described as having spatulate leaves, each with a distinct petiole about an inch long, in whorls of 3, and with margins which were entire or with very few spines. With development of commercial planting in Hawaii, growers came to know the two types as "the rough-shell type" and "the smooth-shell type." In California, they were more commonly referred to as the "ternifolia type" and the "integrifolia type."

The question of the botanical relationship between the two types was raised again by Cheel and Morrison (11). In a bulletin published by them in 1935, the following statement appears: "The edible nuts to be described are obtained from two species of Macadamia, namely, Macadamia ternifolia and Macadamia integrifolia. The latter has been regarded as a variety of the former species, but, in the considered opinion of one of us (E.G.), is a definite species, and must be looked upon as such." Despite Cheel’s opinion, however, M. integrifolia continued to be treated in the literature as a botanical variety of M. ternifolia.

In 1954, Johnson (15) published a paper, which provided the first break in the confusion, which had existed in the true identity of M. ternifolia since the time of its original description by Mueller. To quote Johnson: "There are in cultivation two common species of Macadamia (Proteaceae), both known under the names of "Queensland Nut," "Popple Nut," and variants of the latter. These have been greatly confused, and misleading statements are common concerning the difference or lack of it between them. This has been due to several causes; firstly, semi-juvenile stages of one species resemble the mature stage of the other species in the possession of toothed leaves; secondly, two states of the first species have been described under two different names; and thirdly, the second species has not been named at all.

"The first species under consideration is the type species of the genus, M. ternifolia F. Muell., of which M. integrifolia Maiden and Betche is a synonym. This has toothed leaves in its earlier stages and often flowers in those stages, but in the fully mature stage the leaves are entire (whence the name M. integrifolia). This species is found in Queensland from Mary-borough south of Beechmont and possibly in New South Wales, and various strains are cultivated. The second species, which has toothed leaves at all stages, has been wrongly known as M. ternifolia in New South Wales and overseas. It appears to grow naturally only on the far North Coast of New South Wales and the adjoining part of Queensland, but is also commonly cultivated. Those who know both species as living plants, calling the first M. integrifolia and the second (wrongly) M. ternifolia, have naturally been puzzled by statements (e.g. that of Francis, 1951, p. 91) to the effect that it is doubtful whether M. integrifolia is even varietally distinct from M. ternifolia. These statements are, however, technically quite accurate as made by those whose have (correctly) applied the name M. ternifolia to dentate-leafed states of the first species."

Recognizing that Mueller and Hill had collected the type specimen for M. ternifolia in Queensland and that the specific name had somehow become erroneously attached to a species which is confined almost entirely to New South Wales, he described the latter species as new, giving it the name M. tetraphylla. Thus, according to his interpretation, the spiny-leafed, sessile-leafed, rough-shelled species is M. tetraphylla, and the smooth-leafed, petiolate-leafed, smooth-shelled species is M. ternifolia of which M. integrifolia is a synonym. He noted that the description given by Bentham (8) under M. ternifolia is based on material of both this species and M. tetraphylla; many subsequent interpretations followed this. He stated further, "It seems very likely that M. minor F. M. Bail…with which M. lowii F. M. Bail…appears to be synonymous, is merely a local form or ecotype of M. ternifolia, but field study is desirable to settle this point."

Johnson’s nomenclature quickly came into use among horticulturists in Hawaii and California. The term "ternifolia" was adopted to designate smooth-shelled varieties supplanting the term "integrifolia," and the term "tetraphylla" was adopted to designate rough-shelled varieties supplanting the term "ternifolia." In a paper published in 1955, I (28) proposed adoption of these terms by all horticulturists for the sake of uniformity. In the light of subsequent events, this proposal turned out to be premature, at least in part.

In 1956, Smith (27) arrived at a significantly different interpretation of the ternifolia-integrifolia tetraphylla- minor-lowii complex of species. He agreed with Johnson’s diagnosis of M. tetraphylla, but stated that Mueller’s (8) description and types of M. ternifolia represent the species two forms of which Bailey (6. 7) later described as M. minor and M. lowii. Furthermore, he regarded Maiden’s and Betche’s (18) original concept of M. integrifolia to have been justified and restored it to the status of a valid species. Thus, the complex, as Smith understands it, consists of three species, M. tetraphylla, M. integrifolia, and M. ternifolia, with M. minor and M. low ii reduced to synonymy with the last species.

The first use of Smith’s revised nomenclature in the horticultural literature appears to have been by Eastwood and Kebby (12) in 1957 in a published circular issued by the New South Wales Department of Agriculture. This was soon followed by Hamilton’s (14) paper in the 1958 California Macadamia Society Yearbook that prompted the Editor to include his note explaining the discrepancy between Hamilton’s nomenclature and that of other authors. Possibly, this will signal a return to use of the term "integrifolia" to signify the smooth-shelled, smooth-leafed cultivated Macadamia.

It might be well at this juncture to enumerate the botanical names which, at one time or another, have been considered to represent Australian species of Macadamia, and to remark on their present status.

M. ternifolia F. Muell. This is the name that Mueller (21) gave to his type species in establishing the genus Macadamia from specimens collected at Moreton Bay, Queensland. Later, using the same material, he (22) redescribed the species as Helicia ternifolia, but still later, he (22, 23) returned to the use of M. ternifolia. Quite early (1, 30) the name seems to have become attached to the rough-shelled, spiny-leafed species of New South Wales, an error which continued for almost 100 years, until Johnson (15) determined the New South Wales type to be a species previously undescribed botanically to which he gave the name M. tetraphylla. Johnson (15) thought M. ternifolia to represent the species named M. integrifolia by Maiden and Betche. Smith (27), however, determined the name to apply properly to the species which Bailey (6, 7) described both as M. minor and M. lowii. According to this concept, therefore, this is the valid name for the species which is known by the common names Small-fruited Queensland Nut, Maroochie Nut, and Gympie Nut.

M. integrifolia Maiden and Betche. According to Smith (27), this is the valid name for the species of southern Queensland originally described by Maiden and Betche (18), and commonly known as the smooth-shelled, cultivated Queensland Nut or Macadamia Nut. Possibly, because of mixture of Macadamia material in the herbarium encompassing a wide range of variation in the genus, Maiden and Bechte (19) later revised their diagnosis and reduced the species to the status of a botanical variety of M. ternifolia. It continued to be regarded as a variety until quite recently, although as far back as 1935, Cheel (11) considered it to be a good species and treated it as such. Johnson (15) considered it to represent the original M. ternifolia of Mueller. Smith (27), however, agreed with Maiden and Betche’s original diagnosis and restored it to specific rank.

M. tetraphylla L. Johnson. This name is valid for the rough-shelled, spiny-leafed Macadamia of New South Wales. It was established by Johnson (15) who determined that this species had been known erroneously for nearly 100 years as M. ternifolia and that up to 1954 it had never been given a valid botanical description.

M. youngiana (C. Moore and F. Muell.) Benth. ‘This species was originally described in 1864 by Mueller (22) as a Helicia. It was transferred to Macadamia by Bentham (9), and continued to be so listed by Bentham and Hooker (10) and Bailey (2). In 1889, however, Mueller (23) again recorded it as a Helicia, and it has remained in this genus ever since. The name M. youngiana, therefore, is to be regarded as a synonym of H. youngiana.

M. verticillata (F. Muell.) F. Muell. cx Benth. In 1867, Mueller (22) in redescribing M. ternifolia as H. ternifolia mentioned its affinity to a H. verticillata without describing the latter. Bentham made this in 1880, Bentham and Hooker (10) remarked that the species had been described erroneously from a cultivated plant in the Botanic Gardens at Sydney which proved to be a South African plant Brabeium stellatifolium Linn. Neither the name H. verticillata nor the name M. verticillata has any botanical standing.

M. prealta (F. Much.) Benth. This species was described as a new species of Helicia by Mueller (22) in 1862. It continued to be listed as a Helicia until 1901 when Bailey (5) transferred it to Macadamia. It continues to be classified as a Macadamia species today.

M. whelani (F. M. Bail.) F. M. Bail. Bailey (3) described this species in 1890 as H. whelani. In 1901, however, he transferred the species to Macadamia where it has remained ever since.

M. minor F. M. Bail. This name was given to a new species of Macadamia described by Bailey (6) in 1910. Francis (13), Johnson (15), and Sleumer (26) expressed doubts as to its validity as a separate species. Smith (27) in (956, diagnosed the plant as a variant form of the Gympie Nut or Maroochie Nut, M. ternifolia, and reduced the name to synonymy with that species.

M. lowii F. M. Bail. Originally described as a new species by Bailey (7) in 1911, Francis (13), Johnson (15), and Sleumer (26) expressed doubts as to its standing, also. Smith (27) diagnosed it as another variant of M. ternifolia, and reduced it to the status of a synonym.

M. heyana (F. M. Bail.) Sleum. This species was first described as Helicia heyana by Bailey (5) in 1901. It was transferred to Macadamia by Sleumer (26) in 1955.

From the foregoing, it may be seen that the genus Macadamia, as presently understood, is represented by six species in Australia. These species are M. ternifolia, M. integrifolia, M. tetraphylla, M. prealta, M. whelani and M. heyana.

It is apparent, also, that the dividing line between Helicia and Macadamia is rather finely drawn. In the latest published studies on these genera, those of Sleumer (26) in 1955, the only clear-cut distinction between Helicia and Macadamia appears to be that the ovules are attached at the base of the pericarp in the former and toward the apex of the pericarp in the latter. I am apprised by L. S. Smith, Botanist of the Botanic Museum and Herbarium, Botanic Gardens, Brisbane (personal communication) that he is continuing his studies on the Australian species of Helicia and Macadamia and that Dr. C. V. Rao is making a study of floral anatomy and genetics in the family Proteaceae. These studies presage further realignment of species, with coincidental nomenclatorial revisions, but it seems unlikely that they will affect our present understanding of the species which have been brought into cultivation for their edible nuts. Apparently M. prealta, M. whelani, and M. heyana are so distinct that their entities as good species are beyond question. Nor have they ever been confused with the species of the ternifolia complex. The only question regarding them is whether, properly, they belong in Macadamia.

For the benefit of the reader who may wish to review earlier horticultural literature, I insert a table below indicating the changes that have taken place in the botanical nomenclature (Table 1).

Table 1. Revisions of Macadamia Nomenclature

As I remarked in an introductory paragraph, the reader should be fully aware that there is usually a time lag between the time a botanical revision is published and the time it finds its way into horticultural literature, and should make a point of ascertaining as accurately as possible exactly what species, or horticultural type, he is reading about.

Since the true identity of M. ternifolia seems to have been determined with a certain degree of finality, it seems patently unwise to retain using of the term "ternifolia" to signify the cultivated smooth-shelled Macadamia, so I suggest here a return to use of the term "integrifolia" to designate the type horticulturally. The term "tetraphylla" continues to be eminently satisfactory as a horticultural designation for the cultivated rough-shelled species.

LITERATURE CITED

20. ____ A Census of New South Wales Plants. XX + 216 pp. Sydney. 1916.

22. ____: Fragmenta Phytographie Australiae 2: 91. 1860-61; 3: 7.38. 1862-63; 4: 84. 1864-65; 6:191, 224. 1867-68; 7: 59. 1869-71.

29. ____ Enumeration of Macadamia Species. Calif. Macadamia Soc. Yrbk. 5 :1959.