Idiospermum australiense (Idiospermaceae) - aspects of vegetative anatomy.

Vegetative structural features of Idiospermum, a monotypic ranalean genus rediscovered in 1972, are described and contrasted with comparable features of Calycanthus and Chimonanthus (Calycanthaceae) to note resemblances and differences. The leaf trace pattern and nodal anatomy of Calycanthaceae and Idiospermaceae (one-trace and unilacunar) are very similar. The nodal anatomy of certain highly reduced leaves (scale leaves) of Idiospermum is, however, two-trace and unilacunar. The microscopic wood anatomy of Idiospermum is distinctively different in a number of respects from that of the Calycanthaceae. Although there are similarities, it is suggested that the floral anatomy and vegetative features of Idiospermum set it apart sufficiently from the Calycanthaceae to justify family rank as the Idiospermaceae. THE REDISCOVERY of a new monotypic genus of dicotyledons, named Idiospermum australiense by Blake (1972), is of considerable interest. This rain forest tree of northeastern Australia was assigned by Blake to a new monotypic family, Idiospermaceae. It is an evergreen tree growing to 40 m high and 90 cm in diam. Its simple leathery leaves are petiolate, opposite, decussate (1/2 phyllotaxy), 12-26 cm long, 8-12 cm wide, oblong to elliptic and shortly acuminate with entire margins. The genus is of taxonomic importance because it is a new member of what is frequently referred to as the ranalean complex, essentially equivalent to the subclass Magnoliidae of Cronquist (1968) or to the superorder Annoniflorae of Thorne (1968, 1976). These taxa embrace a group of families viewed as having retained certain features of ancient and possibly ancestral flowering plants. In a previous paper (Wilson, 1976) I reported on the floral anatomy of Idiospermum, comparing it with that of Calycanthusfloridus L. and Chimonanthus praecox (L.) Link. In what follows, the results of certain studies on the vegetative morphology of this plant are presented, again comparing certain features with those of the same species of Calycanthus and Chimonanthus. The features investigated include the scale I Received for publication 14 June 1978; revision accepted 13 October 1978. I am indebted to Mr. B. P. Hyland, Commonwealth Scientific and Industrial Research Organization (Australia), for wood of Idiospermum; to Mr. R. W. Johnson, Queensland Herbarium, for seeds of Idiospermum, and to Dr. J. M. Fogg, Arboretum Barnes Foundation, for material of Chimonanthus. I am grateful to Prof. William T. Jackson, Dartmouth, for the photomicrographs, to Prof. J. P. Poole, Dartmouth, for reading the manuscript, and to Prof. A. E. DeMaggio, Dartmouth, for reading the manuscript and for other assistance. leaves of Idiospermum, the leaf trace pattern in Calycanthus and Idiospermum, and the nodal anatomy and wood of Calycanthus, Chimonanthus, and Idiospermum. MATERIALS AND METHODs-Material of Calycanthus was obtained from greenhouse-grown seedlings and mature plants in cultivation out-ofdoors (Calycanthus floridus L. var. floridus; voucher Wilson 880, in Jesup Herbarium, Dartmouth College), material of Chimonanthus from plants in cultivation, and material of Idiospermum from plants grown in the greenhouse. Wood samples of Idiospermum came from a tree in the native habitat. Procedures included the use of NaOH and chloral hydrate for clearing, especially in the study of scale leaves and nodes. In the study of the leaf trace patterns, terminal parts of shoots were taken, including 5-7 nodes below the apex, but omitting several of the younger uppermost nodes. This involved distances up to 18 cm. The stems were cut into pieces approximately 1.5 cm long, embedded in paraffin, sectioned at 12 ,tm in their proper order, stained with safranin and fast green, and permanently mounted. Three shoots of both Calycanthus and Idiospermum were prepared for study in this way. Following the leaf trace pattern even in mature shoots was made possible by prolonged soaking of the embedded pieces, one end exposed, in a mixture of glycerine and a detergent. A transection of the internodal region of Calycanthus and Idiospermum near the apex of a shoot shows that the vascular cylinder is organized into what has been termed a pseudosiphonostele (Bailey and Nast, 1948). This appears as an essentially continuous ring of primary phloem and primary xylem (Fig. 6, 7) interrupted