Habit and leaf form. Trees; bearing essential oils. Mesophytic. Leaves evergreen; opposite; leathery; petiolate; gland-dotted; aromatic; simple. Lamina entire; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins entire. Leaves without a persistent basal meristem.
Leaf anatomy. The mesophyll with spherical etherial oil cells.
Stem 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 (?). Vessel end-walls scalariform. Sieve-tube plastids P-type.
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.
Geography, cytology. Tropical. Queensland. 2n = 22.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Magnoliiflorae; Laurales. Cronquist’s Subclass Magnoliidae; Laurales. APG 3 core angiosperms; Superorder Magnolianae; Order Laurales (as a synonym of Calycanthaceae).
Species 1. Genera 1; only genus, Idiospermum.