Heliotropium is from the Greek helios for sun and tropaios to turn back because the flowers follow the sun as the flower head uncurls.
Amplexicaule is from the Latin amplexus meaning surrounding and caulus meaning stem and refers to the many branches surrounding the central rootstock.
Blue Heliotrope because it has blue flowers in contrast to the white flowers of most other species in this genus.
Other names:
Clasping Heliotrope (USA)
Herbe bleue (Mauritius)
Purple top
Turnsole
Wild Heliotrope
Wild Verbena
Verveine sauvage (Mauritius).
Summary:
A hairy, low lying, perennial herb with obvious veins on the wavy edged leaves, no petioles, blue flowers, many branched stems and a deep strong taproot system. 150-300 mm tall by 300-2000 mm wide.
Description:
Cotyledons:
Two.
First leaves:
4-6 lance shaped leaves form a rosette.
Leaves:
Dull green. Alternate.
Stipules -
Petiole - None.
Blade - Dull green, oblong to spear shaped, 20-80 mm by 8-20 mm, soft wavy edges. Densely hairy. Obvious hairy veins on the under surface.
Stem leaves - Similar to above.
Stems:
Dull green, 150-1000 mm long, tend to lay on the ground and bend upwards near the end to a height of 150-300 mm, radiate from the central rootstock and are many branched. Hairy.
Flower stem -
Flower head:
Flowers alternate and crowded in 2 rows on the top side of coiled spikes. Spikes in groups of 2 or more at the ends of branches and uncoil as the fruit ripens. When straight the spike is about 100 mm long.
Flowers:
Purple with a yellow centre. Tubular. Scentless.
Bracts - No bracts at the base of the flower.
Ovary - 4 celled, slightly 2 lobed. Convex, hairy. Short style below cone like stigma.
Calyx - Segments 3 mm long. Glandular, hairy. Two types -1) Long and narrow, tapering towards the base. 2) Short and ending in a glandular swelling.
Corolla - Yellow tube with 5 short purple rounded lobes, 4-5 mm long by 5-6 mm wide overall. Hairy outside and a beard of hairs inside the throat.
Perianth -
Sepals -
Petals -
Stamens -
Anthers - Attached near the base of the corolla tube.
Fruit:
Globular and fleshy initially. Becomes wrinkled and warty with age and separates into 2 nutlets with 2 seeds each. Often only 1 seed in each nutlet ripens.
Seeds:
Black, globular, small. Some dormant.
Roots:
Woody rootstock. Strong taproot to more than 1000 mm deep with several layers of horizontal laterals. Root fragments readily sprout when cut by cultivation.
Key Characters:
Short filaments in side corolla tube. Short style below cone like stigma. Beard of hairs inside the corolla throat.
Biology:
Life cycle:
Perennial. Seeds germinate in summer, often with a flush in autumn. A rosette of leaves is formed, then several, long, low lying stems emerge. Flower stems arise from these in spring and flowering starts in November and will continue all summer in moist areas. Older plants are semi dormant in winter and produce a flush of growth in spring and autumn. Mature plants tend to flower in spring and autumn.
Physiology:
Reproduction:
By seed and root buds.
Flowering times:
November to January in SA.
Late spring to summer in Victoria.
In warmer areas some plants may flower from July.
Seed Biology and Germination:
Produces dormant seeds.
Cultivation stimulates dormant seed to germinate.
Vegetative Propagules:
Root buds and fragments.
Hybrids:
Allelopathy:
Population Dynamics and Dispersal:
Much seed is produced. This which will pass through the gut of animals unaffected or stick to the hair or wool for transport. It also moves in water, or mud attached to machinery. It is an occasional contaminant of produce. Root fragments are also a major method of local spread and dispersal following cultivation or road works.
Tends to grow in clumps crowding out all other species.
Origin and History:
South America.
Probably introduced as an ornamental in the late 1800's.
Distribution:
NSW, QLD, SA, VIC.
Habitats:
Climate:
Warm-temperate to sub-tropical.
Soil:
On a wide range of soil types including red calcareous soils, volcanic loams and sandy red earths.
More common on red loamy soils and fallows.
Plant Associations:
Significance:
Beneficial:
Honey plant.
Detrimental:
Weed of sugar cane, roadsides, fallow, pasture, watercourses and disturbed areas.
Fodder but relatively unpalatable to sheep.
Toxicity:
Contains pyrrolizidine alkaloids which are liver toxins and carcinogenic, however they are considered less toxic than those found in Common Heliotrope (H europaeum).
May cause toxaemic jaundice in sheep but field cases are uncommon.
The toxicity is cumulative and symptoms may only develop in the season after consumption or if stock are exposed to Paterson's Curse in the following winter.
Readily eaten by cattle causing frequent deaths especially in young animals.
These toxins also affect humans and it is expected that they will be present in honey taken from infested areas. It is not known what effect on health this may have.
Cultivation will control seedlings but is not effective on mature plants.
Thresholds:
Eradication strategies:
Cutting the root below the crown then pouring diesel onto the fresh cut may control single plants. Hormone herbicides, picloram, amitrole and glyphosate provide useful levels of control.
Establish competitive pastures and supply adequate fertiliser.
Herbicide resistance:
Biological Control:
Related plants:
Common Heliotrope (Heliotropium europaeum)
Rough Heliotrope. (Heliotropium asperrimum)
Smooth Heliotrope (Heliotropium curassavicum)
(Heliotropium indicum)
(Heliotropium supinum)
Plants of similar appearance:
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P127. Photo.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P712. Diagram.
Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P122-123.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #635.1.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P333-335.
Acknowledgments:
Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.