Prostanthera spinosa

Spiny Mintbush

There are five populations of Prostanthera spinosa known from confirmed records, and possibly several other small populations from anecdotal sightings in Banyabba Nature Reserve
The confirmed records include locations within Fortis Creek National Park and Banyabba Nature Reserve
All known populations are within a linear range of 16-20 km
Available information suggests that each population comprises tens to hundreds of individuals; not all of these individuals may be mature
The main threats include:
- - frequent fire
  - environmental stochasticity due to the species' geographically restricted distribution and small local populations
Standing plants are apparently killed by fire and, while the species may have a soil seed bank, its germination cues and seed longevity are unknown
Fire history data for the Banyabba - Fortis Creek area indicate that single fires may burn the entire NSW range of the species, and that most of the range of P. spinosa has been burnt in 2-4 extensive wildfires within a 15 year period from 1986/87 to 2002/03
"High frequency fire resulting in the disruption of life cycle processes in plants and animals and loss of vegetation structure and composition" is listed as a Key Threatening Process under the Threatened Species Conservation Act
In view of the above the Scientific Committee is of the opinion that Prostanthera spinosa is likely to become endangered in NSW unless the circumstances and factors threatening its survival or evolutionary development cease to operate

Etymology:

Prostanthera is derived from the Greek for an appendage
The specific epithet (spinosa) is derived from the Latin spinosus meaning "thorny"

Flowers:

It has mauve to white flowers
Its flowers occur singly in the leaf axils, they are pale mauve to lilac to white with orange-brown streaks or spots on the lower inside petal that is 2–3 mm (0.079–0.118 in) long.
The bracteoles remain to flower maturity are 0.9–2 mm long and 0.2–0.3 mm wide
Flowering occurs from July to December

Fruit:

Leaves:

Aromatic foliage
The small leaves are thickly hairy or with occasional hairs, mostly on the petiole
The leaf is narrowly egg-shaped to broadly elliptic or trullate
1.5–6 mm long, 1–3 mm wide
The petiole 0.4–1 mm long
The leaves are darker on the upper surface, paler on the underside
Smooth or with firm, spreading hairs below on the midrib and profusely covered with glands
The leaf margins entire or slightly rolled under
Underside veins obscure
Ending in a rounded apex
On a petiole 0.4–1 mm long

Stem & branches:

Spiny stems and aromatic foliage
The aromatic branches may be sparsely or moderately densely hairy
Either upward spreading, straight or curled hairs 0.2–1 mm long, or smooth with a few hairs at the nodes
Consistent decussate spines 6–16 mm long

Roots:

Habit:

A small, rigid, upright shrub with a scrambling habit mostly semi-prostrate
Usually 0.2–2 m high

Habitat:

Occurs in the Grampians in rocky locations on shallow, sandy soils
In South Australia it is found growing near watercourses mostly in loamy-sand over limestone or sandstone

Distribution:

Endemic to south-eastern Australia

Additional notes:

Taxonomy and naming

The species was formally described in 1855 by Victorian Government Botanist Ferdinand von Mueller, based on plant material collected from "rocky declivities in springs near the Grampians"
The description was published in Hooker's Journal of Botany and Kew Garden Miscellany

Sources of information:

Prostanthera spinosa

Contents:

Location & distribution maps

Phylogeny & links to associated information:

Plant information