Praxelis spp.

praxelis

Attracts Pollinators Attracts Butterflies Drought Tolerant

Overview

Praxelis is a genus of erect annual to short-lived perennial herbs in the daisy family (Asteraceae), native to South America. The most prominent species, Praxelis clematidea, has spread as an aggressive weed across parts of Asia, the Pacific, and northern Australia. Plants grow 1.5-3 ft (45-90 cm) tall on branched, hairy stems, with opposite, coarsely toothed leaves that give off a strong, unpleasant smell when crushed. From spring through autumn, and nearly year-round in warm climates, the stems carry fluffy, brush-like flower heads of small lilac to purple-blue florets, much like those of the related mistflowers (Ageratum). Each head produces many small seeds tipped with white bristles that carry on the wind, allowing rapid colonisation of bare ground. The genus grows on disturbed, open soils in pastures, crops, plantations, and roadsides, and Praxelis clematidea is a declared or regulated weed in several countries, including Australia. One limitation for any garden use is exactly this weediness: the plants seed prolifically and spread aggressively.

Native Range

Praxelis is native to South America, particularly Brazil, Argentina, Paraguay, and neighbouring countries. Beyond its native range Praxelis clematidea has naturalised widely in tropical and subtropical Asia, the Pacific islands, and northern Australia, where it colonises disturbed and cultivated land.

Suggested Uses

The genus has no recognised horticultural use and is regarded as an environmental and agricultural weed. Praxelis clematidea is studied mainly in the context of weed science and biosecurity. It is included here for identification rather than for planting.

How to Identify

Identify Praxelis by its upright, hairy stems, opposite coarsely toothed leaves with a pungent smell when crushed, and fluffy lilac to purple-blue flower heads lacking ray florets. It closely resembles blue billygoat weed and mistflower, but the leaves are arranged oppositely and the bracts around each flower head are pointed and arranged in spirals. The plumed, wind-borne seeds are a further sign.

Appearance

Size & Dimensions

Height1'6" - 3'

Width/Spread1' - 2'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~20 weeks

Spring Summer Fall

Flowering occurs over a long season, from spring through autumn in warmer temperate areas and nearly year-round in the tropics. The brush-like lilac flower heads open continuously, and each is quickly replaced by a head of plumed seeds. A single plant can flower and seed within a few weeks of germinating.

Detailed Descriptions

Flower Description

lilac to purple-blue

Foliage Description

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 Range5.0 - 7.5(Neutral)

357912

Soil Types

sand loam clay

Drainagewell drained

Water & Climate

Water Needs

Low

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Praxelis grows in full sun on a wide range of light, disturbed soils across an acidic to neutral pH of about 5.0 to 7.5, tolerating poor and dry ground. It germinates readily on bare soil and completes its life cycle quickly, self-sowing in large numbers. The genus is frost-tender and behaves as a warm-season annual at the edge of its range, dying with the first hard frost. Because Praxelis clematidea is a declared or regulated weed in several regions, its cultivation, sale, or movement is prohibited in those areas. Where it appears as a volunteer it is usually controlled rather than grown. No special care is needed for the plant to persist on open ground.

Pruning

No pruning is practised, as the genus is treated as a weed rather than a cultivated plant. Where control is wanted, plants are removed before the flower heads set seed to limit spread. Repeated removal of seedlings is needed because of the large soil seed bank.