Myrtle-leaved Milkwort

Polygala myrtifolia L.

Synonyms -

Family: Polygalaceae.

Names:

Polygala is the Latin from of the Greek polygalon derived from poly meaning many or much and gala meaning milk and refers to the ancient belief that animals eating these plants produce more milk.
Myrtifolia is Latin for Myrtle-leaved.

Other Names:

Bellarine Pea
Butterfly Bush - because the flowers look like butterflies.
Myrtle-leaf Milkwort
Myrtleleaf Milkwort
Parrot Bush
September Bush - because it tends to flower in September
Sweet Pea Shrub (NZ)

Summary:

Myrtle-leaved Milkwort (Polygala myrtifolia) is a perennial, erect, bushy shrub 1.5-4 m high with crowded light green elliptic leaves that are 10-50 mm long. The clustered, pink to purple and white flowers are pea-like but the keel petal is crested and there are only 8 stamens. The fruit is a circular capsule.
Native to South Africa, it is a garden escape now invading bushland, particularly in sandy coastal areas. It flowers in spring and early summer.

Description:

Cotyledons:

Two.

First leaves:

Leaves:

Alternate. Water repellent when mature.
Stipules - None.
Petiole - Short.
Blade - Pale green to yellowish, elliptic to egg-shaped or oblong, flat, (10)20-30(50) mm long x (4)8-10(20) mm wide. Same colour on top and below. Tip rounded, blunt or slightly indented. Edges curved and entire. Hairless to sparsely hairy and sometimes with short wispy hairs on the margins.

Stems:

Purplish or reddish tinged often with short, curled hairs when young. Light brown to grey, smooth, hairless and woody when old. Remnants of leaf stalks persist on the older stems. 1.4-4 m long.
Doesn't coppice.

Flower head:

Short, dense and leafy, 10-50 mm long clusters (racemes) at the ends of branches with a few flowers on 5-10 mm long stalks (pedicels) with 2-3 tiny, 1 mm, egg shaped bracts at the base.

Flowers:

Purple to pink and white, pea-like, 10-20 mm long with the lowest petal with a forward pointing brush like crest and a lower white petal with a purple blotch and purple wing petals with green veins. Bisexual.
Ovary -
Style - curved or hooked.
Sepals - 5, free. 3 outer sepals are green, lance-shaped and boat-shaped, 4-5 mm long. Inner 2 sepals are petal-like wings and streaked greenish, purple and white with purple edges and inner face, egg shaped, 10-15 mm long x 10-15 mm wide.
Petals - 5 but appears to be 3 as 2 are fused with the keel. Keel is white with a purple tip, 10-15 mm long, hairy near the short claw and has a white crest with 2 much branched appendages 4-6 mm long. Keel is joined to the staminal tube at the base. Side petals are small and 2 lobed.
Stamens - 8.
Anthers - 8, opening by a pore at the top.

Fruit:

Egg shaped to circular or heart shaped, flat, narrowly winged, flattish capsule, 7-10 mm diameter. 2 celled. 2 seeded. Initially green and turning brown when ripe.

Seeds:

Dark brown, hairy, oblong, 5 mm long. They have an appendage near the scar (caruncle).

Roots:

Woody branching taproot and laterals that are shallow and mostly in the top 300 mm of soil. Doesn't sucker or coppice.

Key Characters:

Erect shrub.
Leaves alternate, elliptic to broadly elliptic and usually >6 mm wide.
Flowers purple to pink and white.
Flowers in short terminal racemes.
Flowers >8 mm long.
8 Stamens
Capsule ovate.
Seeds with caruncle (appendage near the scar)
Seeds with hairs not lengthening into a coma (tuft).
Adapted from L. Murray, Flora of NSW, J. Wheeler and John Moore.

Biology:

Life cycle:

Perennial.
Seeds tend to germinate in autumn but can germinate at any time of year moisture is available. Increased germination follows fire, disturbance and denudation. Germination can occur in heavy shade and under light mulch. The seedlings grow quickly and can flower when they are less than 500 mm tall. It grows mainly over the cooler and wetter winter and spring periods. The mature plant flowers mainly in spring to summer to produce seed for an autumn germination. High levels of seed production and seed dormancy results in significant soil seed banks.

Physiology:

Tolerates drought, fire, wind, sun, shade, salt, light frosts.
Mature leaves are water repellent.

Reproduction:

By seed.

Flowering times:

August to December in WA.
Summer in SA.
Most of the year in Victoria with a flush from August to December.
Most of the year in NSW with a flush in September to October.
January to December in New Zealand.

Seed Biology and Germination:

It has dormant seed that can remain viable in the soil for at least 3 years.
Seeds germinate readily after fire, soil disturbance or canopy removal. The seeds will germinate in full sun or shade.

Vegetative Propagules:

None.

Hybrids:

There are 2 main varieties:
Polygala myrtifolia var. myrtifolia is the commonly weedy variety with purple flowers and usually surrounded by seedlings.
Polygala myrtifolia var. grandifolia is sold in nurseries and was thought to be sterile but can set some seed. It has bright magenta flowers and doesn't appear to have naturalised.

Allelopathy:

Population Dynamics and Dispersal:

It can build up large populations rapidly.
Spread by water, ants and birds.
Medium distance dispersal by dumping of garden refuse, earthmoving, beach equipment like boats and towels, water and birds.
Local dispersal by ants and water.
Up to 2000 seedlings per square metre can germinate and this drops to 12-30 per square metre after a year.
Fire stimulates germination but is not required for germination.

Origin and History:

Native to the Cape region of South Africa.
Planted as an ornamental and has naturalised in southern Australia.

Distribution:

NSW, QLD, SA, TAS, VIC, WA.
Jarrah forest, Swan coastal plain and Warren regions of WA.
New Zealand, Hawaii.

Courtesy Australia's Virtual Herbarium.

Habitats:

Heathland, heathy woodland, shrublands, grasslands, dry sclerophyll forest, riparian, rock outcrops, dry coastal areas, mallee shrub land.

Climate:

Temperate coastal.

Soil:

Brown-orange or grey sand, loam, sand dunes, coastal bluffs.

Plant Associations:

Coastal heath species.

Significance:

Beneficial:

Ornamental.

Detrimental:

Invasive weed of coastal areas, roadsides, winter wet gullies and creeklines.
It can forms dense, mixed-aged thickets preventing most other species establishing.

Toxicity:

Not recorded as toxic.

Symptoms:

Treatment:

Legislation:

Banned in New Zealand.

Management and Control:

Grazing and mowing provide control.
Avoid transporting green waste and soil containing seed to clean areas.
Don't burn or disturb partially infested areas unless follow up control is planned.

Thresholds:

Eradication strategies:

Seedlings and small plants can be removed manually. Larger plants can be cut off close to ground level or mown and usually don't regrow. Burn or deeply bury material that has ripe fruit or seed. Fire will kill small plants and if intense enough it will also kill larger plants and encourage seeds to germinate. These need controlling in the following 3 seasons. Burning without follow up control usually leads to increased infestations.
100 mL glyphosate(450g/L) in 10 L water applied as an overall spray provides control. Spray infestations in winter to create dead material for a hot burn in spring if possible. Sprays are preferred in areas where disturbance may lead to soil erosion.

Herbicide resistance:

None reported.

Biological Control:

Related plants:

Broom Milkwort (Polygala virgata) is another species which has become weedy. It differs in having narrower leaves and elongated sprays of flowers.
Polygala x dalmaisiana is a similar garden plant that doesn't appear to be invasive.

Plants of similar appearance:

Seedlings of Coast Teatree (Leptospermum laevigatum) and the native Coast Beardheath (Leucopogon parviflorus), Alyxia buxifolia and eastern states Pultenaea daphnoides also look similar to Myrtle-leaved Milkwort seedlings.

References:

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P505.

Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).

Blood, K. (2001). Environmental weeds: a field guide for SE Australia. (CH Jerram & Associates, Australia). P70-71. Photos.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).

Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume 3. P6. Diagram.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (2007). Western Weeds. A guide to the weeds of Western Australia. (Second Edition). Plant Protection Society of Western Australia, Perth, Western Australia. P212. Photo.

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #805.3.

Moore, J.H. and Wheeler, J.R. (2008). Southern Weeds and their Control. (Second Edition). Department of Agriculture and Food Western Australia. P198-199. Photos.

Muyt, A. (2001). Bush Invaders of South-East Australia: a guide to the identification and control of environmental weeds found in South East Australia. (R.G and F.J. Richardson, Australia). P207-208. Photos.

Paczkowska, G. and Chapman, A. (2000). The Western Australia flora: a descriptive catalogue. (Wildflower Society of Western Australia (Inc), the Western Australian Herbarium, CALM and the Botanic Gardens & Parks Authority). P459.

Randall, J.M. and Marinelli, J. (1996) Invasive Plants. (Brooklyn Botanic Gardens Inc. Brooklyn). P. Photo.

Roy, B., Popay, I., Champion, P., James, T. and Rahman, A. (1998). An Illustrated Guide to Common Weeds of New Zealand. (New Zealand Plant Protection Society). P232. Photo

Stucky, J.M. (1981). Identifying Seedling and Mature Weeds Common in the Southeastern United States. (The North Carolina Agricultural Research Service and The North Carolina Agricultural Extension Service, North Carolina State University, Raleigh).

Wheeler, Judy, Marchant, Neville and Lewington, Margaret. (2002). Flora of the South West: Bunbury - Augusta - Denmark. (Western Australian Herbarium, Bentley, Western Australia). P800. Diagram.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 for more information.