Giant-flowered broom

Botanical name:Carmichaelia williamsii
Synonyms: None
Common name(s): William’s broom, Giant-flowered broom, Native broom

About:
Carmichaelia williamsii is one of New Zealand’s most spectacular native brooms and the only species with large pale yellow flowers. This rare coastal shrub forms an upright mass of broad, flattened green stems and produces impressive clusters of blooms through winter and spring. Once widespread along parts of the eastern North Island coast, it now survives mainly on offshore islands and a few mainland sites.

Natural habitat:
Open coastal forest, scrub, cliff faces, talus slopes and steep coastal hillsides.

Growing environment:
Thrives in full sun and free-draining soils. Best suited to warm coastal climates with good air movement. Tolerates drought, wind, salt exposure, frost and occasional snow but dislikes prolonged humidity and poorly drained sites.

Endemic distribution:
Endemic to New Zealand. Naturally found in the northern and eastern North Island, from northern offshore islands including the Poor Knights and Alderman Islands south to East Cape. Only a few mainland populations remain.

Height:
2–4 m

Width:
2–4 m

Flowering:
July–October, with occasional flowers throughout the year

Fruiting:
Present throughout the year

Uses:

• Coastal restoration planting
• Native bird gardens
• Feature shrub for dry gardens
• Coastal revegetation projects
• Habitat and food source for native pollinators
• Conservation plantings of rare species

Appearance:

Growth habit:
Robust upright to spreading shrub with a dense framework of broad, flattened green stems.

Branches:
Thick, flattened cladodes 5–12 mm wide, green to yellow-green, strongly grooved and almost leafless. Lower branches often arch or droop gracefully.

Leaves:
Usually absent on mature plants. Small fleshy leaves are mainly found on seedlings, shaded shoots and vigorous new growth.

Flowers:
Among the largest flowers of any New Zealand native broom. Pea-shaped blooms up to 25 mm long, pale yellow to creamy yellow, often marked with striking purple or maroon veins. Produced in clusters of up to six flowers.

Fruit:
Flattened brown pods 23–34 mm long containing 5–15 hard orange-red seeds, usually mottled with black.

Ecology:
Flowers are primarily pollinated by native honeyeaters such as tūī and bellbirds. Seeds may be dispersed by wind and granivorous birds. The species is vulnerable to seed predation by rats and browsing by introduced mammals.

Associated habitats:
Coastal scrub, cliff communities, open forest margins, talus slopes, rocky coastal hillsides and island ecosystems.

How to grow:
Plant in full sun in a free-draining position. Performs best in coastal gardens with low humidity. Although reasonably hardy, plants are often short-lived, typically surviving 5–15 years. Maintaining replacement plants from seed is recommended. Avoid root disturbance once established.

Propagation:
Easy from fresh seed or hardwood cuttings. Germination is greatly improved by scarifying seed and soaking it overnight before sowing.

Cultural use:
Named after Bishop William Williams, who collected some of the earliest known specimens. It is an important component of northern New Zealand coastal ecosystems and one of the country’s most distinctive native shrubs.

Garden value:
A truly outstanding ornamental native. Its broad green stems, spectacular pale-yellow flowers and winter flowering season make it unlike any other New Zealand broom. Ideal as a specimen shrub in coastal and dryland gardens where its unusual form and blooms can be fully appreciated.