Carmichaelia, commonly known as New Zealand brooms, is a genus of 24 flowering plant species in the legume family Fabaceae (order Fabales). The genus is nearly entirely endemic to New Zealand, with 23 of its species native there and only one, Carmichaelia exsul, occurring on Lord Howe Island — almost certainly the result of long-distance dispersal from New Zealand.
The plants are strikingly adapted to their environment: mature individuals are typically leafless, with photosynthesis carried out by flattened green stems (cladodes) that replace the function of leaves. The leaves themselves are reduced to fused stipule scales. Growth habit spans a wide range, from small trees and tall shrubs down to prostrate mat-forming plants only a few centimetres in height.
Carmichaelia species are distributed throughout New Zealand, though the eastern South Island is a particular centre of diversity, with 15 species found nowhere else. Most species occupy a restricted range within the country, favouring disturbed and open habitats: shallow, nutrient-poor soils, alluvial terraces, river banks, rock outcrops, and sites exposed to drought or frost.
Taxonomically, Carmichaelia sits within the clade Carmichaelinae alongside Clianthus (kākābeak), Montigena (scree pea), and Swainsona. Several formerly separate New Zealand genera — Chordospartium, Corallospartium, Notospartium, and Huttonella — have been merged into Carmichaelia following modern molecular revisions. The most widespread species, Carmichaelia australis (common native broom, mākaka), is a shrub reaching 2–8 m and serves as a reference point for the genus; it is now assessed as At Risk – Declining under the New Zealand Threat Classification System. Despite superficial resemblance, New Zealand brooms are not closely related to the European common broom (Cytisus scoparius), which has been introduced to New Zealand and is classified as a noxious weed.
Etymology
Carmichaelia was named in honour of Captain Dugald Carmichael (1772–1827), a Scottish army officer and botanist who collected and studied plants in New Zealand during the early 19th century. The species epithet australis, used for the most widespread member of the genus, is Latin for "southern."
Distribution
Carmichaelia species are found throughout New Zealand from coastal to montane zones, with the eastern South Island representing the highest concentration of diversity — 15 species are endemic to that region alone. Most species have restricted ranges within New Zealand. The exception to the genus's New Zealand endemism is Carmichaelia exsul, native to Lord Howe Island, which was presumably dispersed there from New Zealand. Typical habitats include river terraces, stream banks, rock outcrops, tussock grassland margins, colluvium, and disturbed ground on shallow or drought-prone soils.
Ecology
Plants colonise open, disturbed habitats including alluvial soils, talus, fan-toe slopes, grey scrub margins, and the edges of forest. Flowering typically occurs from October to February (austral spring–summer), with fruiting from November to May. Seeds are small, hard, and often orange or red; dispersal is thought to occur via wind and granivory. The flattened cladodes function as the primary photosynthetic organs in mature plants, an adaptation to the exposed, often nutrient-poor environments the genus favours.
Conservation
Several Carmichaelia species are threatened or at risk under the New Zealand Threat Classification System (NZTCS). Carmichaelia australis, once assessed as Not Threatened (2004–2017), was reclassified as At Risk – Declining in the 2023 assessment, with qualifiers indicating ongoing pressure from habitat loss, pastoral farming, and other factors. The broad genus-level trend of range contraction reflects the widespread loss of the lowland and montane open habitats that New Zealand brooms depend on.
Propagation
Carmichaelia australis and related species are noted as easily grown from seed and hardwood cuttings. Seeds are hard-coated and may benefit from scarification to improve germination.
