Cartonema is a small genus of flowering plants in the dayflower family (Commelinaceae), order Commelinales, comprising seven accepted species entirely restricted to Australia and the nearby Trangan Island in Indonesia's Aru Islands. It is the earliest-diverging lineage within Commelinaceae and stands apart from all other members of the family in several structural features: it lacks internal raphides (needle-like calcium oxalate crystals) and glandular microhairs, which are otherwise universal within the family. These distinctive characters once prompted botanists to segregate it into its own family, Cartonemataceae, but molecular phylogenetic analysis together with shared anatomical traits has firmly placed it within Commelinaceae.
Plants in the genus are either annuals or perennials; perennial species sometimes produce tubers. The leaves are spirally arranged, linear, stalkless, and covered in glandular hairs — a character rare elsewhere in the family. Flowers are borne in spikes or racemes arising either terminally or along the main shoot. As in all Commelinaceae, the basic inflorescence unit is a cincinnus (scorpioid cyme), but in Cartonema each cincinnus is so reduced that it bears only a single flower. The flowers are bisexual and radially symmetrical, with free yellow (rarely pink) petals, free glandular-hairy sepals, and six fertile stamens whose anthers dehisce longitudinally. The ovary comprises three carpels, the fruit is a three-valved capsule, and seeds bear a punctiform hilum. The diploid chromosome number is 2n = 24.
Individual species are distributed across discrete Australian regions: northern Australia, the northern Northern Territory, northeastern and northwestern Queensland, southwestern Australia, and extending into New Guinea, reflecting the genus's long isolation on the Australian continent.
Distribution
The genus is endemic to Australia and, at its northeastern edge, extends to Trangan Island in Indonesia's Aru Islands. Within Australia, species occur across the northern and northeastern mainland (northern Northern Territory, northern and northeastern Queensland), northwestern Queensland, and southwestern Australia, with one species (Cartonema parviflorum) also reaching New Guinea.
Taxonomy Notes
Cartonema was historically treated as the sole genus of its own family, Cartonemataceae, owing to its absence of raphides, absence of glandular microhairs, and yellow-flowered radial symmetry — all departures from the Commelinaceae norm. DNA sequence analyses and shared anatomical evidence subsequently supported its placement as the earliest-diverging lineage within Commelinaceae, making Cartonemataceae a synonym.
