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Swainsona spp.

Swainson pea

Overview

Swainsona spp. is a genus of about 85 species in the legume family (Fabaceae), with all but one species endemic to Australia and a single species reaching New Zealand. The genus spans annual herbs, herbaceous perennials, and small subshrubs, growing from prostrate mats to upright stems 4-40 inches (10-100 cm) tall. Leaves are pinnately compound with 5 to 21 leaflets, often grey-green and covered in downy hairs that reduce water loss in dry habitats. Flowers are pea-shaped (papilionaceous) and held in upright racemes, ranging across red, pink, purple, mauve, white, and yellow depending on species; S. formosa, the Sturt's Desert Pea, carries blood-red blooms with a black central boss. Flowering follows rainfall and is concentrated in spring across most of the range. Seeds form in inflated or flattened pods typical of the family. Several species accumulate the alkaloid swainsonine, which is toxic to grazing livestock. Many Swainsona spp. species are adapted to seasonally dry inland soils and are short-lived, dying back or perishing after seed set, which limits their persistence in cultivation outside well-drained, low-humidity conditions.

Native Range

Swainsona spp. is almost entirely Australian, with species spread across every mainland state from coastal districts to the arid interior. A single species, S. novae-zelandiae, occurs in New Zealand.

Suggested Uses

Used in native and water-wise gardens, rockeries, and containers across Australia, with the red-flowered S. formosa grown as a sprawling ornamental and in raised or hanging displays. Inland species feature in revegetation of dry, open ground.

How to Identify

Recognised by pinnately compound leaves with an odd terminal leaflet and pea-shaped flowers held in erect racemes above the foliage. The upper standard petal is rounded and often reflexed, and the keel curves to a blunt or beaked tip. Inflated to flattened pods and a five-toothed calyx separate Swainsona spp. from similar Australian legumes.

Appearance

Size & Dimensions

Height4" - 3'4"

Width/Spread8" - 3'4"

Colors

Flower Colors

red

Foliage Colors

Bloom Information

Bloom Period

~4 weeks

Spring

Most species flower in spring (September-November in the southern hemisphere), and desert species bloom opportunistically within weeks of significant rainfall at any season. Flowering lasts several weeks, after which plants set seed and many annual or short-lived species die back.

Detailed Descriptions

Flower Description

red, pink, purple, mauve, white, or yellow

Foliage Description

grey-green to green

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-12 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.0 - 8.0(Neutral)

357912

Soil Types

sand loam

Drainagewell drained

Water & Climate

Water Needs

Low

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Across the genus, Swainsona spp. grows in full sun and sharp-draining sandy or loamy soils, reflecting origins in open inland Australian habitats. Most species tolerate extended dry periods once established and are intolerant of waterlogging, which causes rapid root rot. Soil pH from about 6.0 to 8.0 suits the group. Frost tolerance varies: inland species withstand light frost, while subtropical species are tender. Seed germination is improved by scarification or brief hot-water treatment to break the hard coat. Humidity and heavy clay are the main limits to growing the genus outside its native range.

Pruning

Little pruning is needed. Spent flower stems can be removed after seed set, and perennial species respond to a light trim that encourages denser branching. Annual species complete their cycle in one season and are not pruned.