heliotropium or blue heliotrope or Purpletop
Heliotropium amplexicaule or Purpletop aka Blue Heliotrope

Blue Heliotrope (Heliotropium amplexicaule)

Blue Heliotrope is also known as Purpletop. It is easy to identify as it has clusters of small mauve, yellow-centred flowers along a coiled stem with hairy soft green foliage and a pungent odour. It grows over the Summer months, and is a branching erect biennial.

Blue Heliotrope is extremely drought-hardy, which increases its ability to persist and spread, and if left un-checked, it will rapidly populate bare ground.

Blue Heliotrope can be found in a wide range of habitats, and can reproduce from both seed and root fragments. It spreads aggressively, as it produces many sticky seeds that adhere to animals and machinery.

The spreading plant rapidly populates cropping and pasture paddocks regenerating from fragments of its strong tap root and from the sticky seed heads which commonly hitch a ride on machinery, native animals and livestock.

Blue Heliotrope contains high levels of alkaloids and is toxic to all livestock. It causes liver damage and potentially, stock deaths. Although animals tend to only graze the weed when hungry and alternative pasture is scarce, the weed is toxic both fresh and dried

Blue Heliotrope contains pyrrolizidine alkaloids (PAs) but isn’t very palatable to livestock, but it will be eaten if no other feed is available.

Livestock that eat a lot of either dry or fresh plants or their seeds in stock feed, can develop liver damage and have reduced productivity. Horses are the most susceptible.

After you read this, you will be able to:

  • Identify Blue Heliotrope or Purpletop .
  • Know the habitat of Blue Heliotrope.
  • Know the best options to control Blue Heliotrope or Purpletop.


How to Identify Blue Heliotrope.

Flowering depends on rainfall, but tends to start in November, and then continues through the Summer until March. I areas that don’t get frosts this weed can grow and flower at any time of the year after rain. In the Spring and Autumn, existing plants produce a flush of new growth, and flower profusely at these times. In warmer areas, plants may flower and set seed even earlier than this.

This weed does not like frost, so in areas like the ACT it tends to die off in Winter, and regenerates from its root system in the following spring.

Category: Broadleaf (Dicot).

Flower: The flowers are bluish-purple with yellow centres.

Height: It grows to a height of between 15–30 cm.
Leaf length: Purpletop has distinct spear shaped leaves which are a dull green colour. The stem, like the leaves are hairy.

Leaf Width: The leaves are 15-20 mm wide, and have a toothed edge.

Leaf ID: Blue heliotrope is hairy along its edges.

Reproduction: Purpletop can reproduce from both seed and root fragments.

Comments: It is in the same family as Paterson’s curse.

Habitat:  More on lawn and turf grass weeds is in our weed ID chart.


How to control Blue Heliotrope.

Both cultural and chemical control will control Blue Heliotrope or Purpletop in your lawn and turf.

Cultural control:

One of the best ways to prevent establishment of Purpletop is by maintaining a vigorous turf cover. This means good practices such as mowing at the right height and fertilizing you turf properly, ensure that your grass is able to outcompete this weed. By reducing thin and bare areas, you can reduce the opportunity for this weed to germinate and establish.



Chemical control of Blue Heliotrope:

Blue Heliotrope is difficult to control, and its hairy leaves limit herbicide uptake. Many herbicides only kill the top of the plant, which means it then re-shoots from the remaining root system.

Systemic herbicides do however, work well against Blue Heliotrope as they destroy their root system. As with all herbicides avoid spraying this weed when it is under stress, and aim to apply when the weed is actively growing and beginning to flower.


Pre-Emergent Herbicide.

For 6-months weed germination prevention, we recommend Pre-Emergent Herbicides, such as ProForce Onset 10GR.


Post-Emergent Herbicide.

Non selective options include Glyphosate (Rapid Fire 800). If you use this and water quality is an issue then we recommend the use of ProForce Manta Ray.