The families of flowering plants

L. Watson and M.J. Dallwitz

Idiospermaceae S.T.Blake

~ Calycanthaceae.

Habit and leaf form. Trees; bearing essential oils. Mesophytic. Leaves persistent; opposite; leathery; petiolate; gland-dotted; aromatic; simple. Lamina entire; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins entire. Leaf development not ‘graminaceous’.

Leaf anatomy. The mesophyll with spherical etherial oil cells.

Axial (stem, wood) anatomy. Nodes unilacunar (with a single trace). Cortical bundles present (when young with four inverted vascular bundles in the pericycle or cortex). Secondary thickening developing from a conventional cambial ring (?).

The vessel end-walls scalariform.

Reproductive type, pollination. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’ (in 1–3 flowered inflorescences). Inflorescences terminal, or axillary. Flowers bracteate (the peduncle with several decussate bracts); regular; acyclic. The perianth acyclic and the androecium acyclic, or the perianth acyclic, the androecium acyclic, and the gynoecium acyclic. Floral receptacle markedly hollowed. Free hypanthium present.

Perianth sequentially intergrading from sepals to petals, or petaline; 30–40 (spiralled, the outer members the largest and deciduous, the other 15–18 retained); free; white (initially), or red (later); persistent (the inner 15–18 members), or deciduous (the outer members).

Androecium 25–100 (‘many’, at the rim of and within the hypanthium). Androecial members maturing centripetally; free of the perianth; free of one another; spiralled. Androecium including staminodes (the outer 13–15 members fertile, the remainder sterile). Staminodes about 20–40 (becoming smaller acropetally); internal to the fertile stamens; petaloid to non-petaloid (more or less tepal-like). Stamens 13–15; laminar to petaloid (more or less tepal-like, not obviously filantherous, thick, triangular). Anthers adnate; dehiscing via longitudinal slits; extrorse (dorsal, more or less basal); appendaged. The anther appendages apical (in the form of the inflexed tip of the stamen blade). Pollen shed as single grains. Pollen grains aperturate; 2 aperturate (bisulcate).

Gynoecium 1(–3) carpelled. The pistil when monomerous, 1 celled. Gynoecium monomerous, or apocarpous; of one carpel, or eu-apocarpous; superior (the receptacle/hypanthium cupular and enclosing the gynoecium, but the latter — and subsequently the pericarp — remaining free). Carpel more or less non-stylate; apically stigmatic (with a subsessile, obliquely terminal stigma); 1(–2) ovuled. Placentation marginal to basal. Ovary sessile. Ovules non-arillate; anatropous; bitegmic.

Fruit strictly non-fleshy (but enclosed in the enlarged, almost closed, internally fleshy receptacle); an aggregate (when not monomeric), or not an aggregate. The fruiting carpel indehiscent. Fruit enclosed in the fleshy hypanthium (the latter becoming hard outside, fleshy within). Dispersal unit the flower (ie. the internally fleshy receptacle/hypanthium plus persistent perianth members and the free but enclosed fruit). Seeds non-endospermic. Embryo well differentiated (filling the seed). Cotyledons 3–4; fleshy, peltate.

Physiology, phytochemistry. Sieve-tube plastids P-type.

Geography, cytology. Tropical. Queensland. 2n = 22.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Magnoliiflorae; Laurales. Cronquist’s Subclass Magnoliidae; Laurales. APG III core angiosperms; Superorder Magnolianae. APG IV Order Laurales (as a synonym of Calycanthaceae).

Species 1 (Idiospermum australiense). Genera 1; only genus, Idiospermum.

General remarks. Apart from the record of scalariform vessel end-walls, this description of Idiospermum differs from that of Calycanthaceae (q.v.) only in the fewer, non-stylate carpels and the embryo with 3–4 cotyledons!.

Illustrations. • I. australiense: Blake,1972 (

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 5th March 2018.’.