Stachytarpheta mutabilis

Stachytarpheta mutabilis.

Pink or Red Snakeweed is native to Mexico and the Caribbean area.
It is naturalised, and a weed, in S.E. Queensland.

They are perennial herbs or sub-shrubs growing up to 1 m high.
There are dense short white hairs on the stems.

The opposite leaves, up to 12 cm long, are on hairy, partially winged petioles.
The leaf edge, except near the base, is finely toothed.
Both surfaces have pale hairs especially dense on the veins underneath.
The veins are depressed on the upper surface.
The upper surface has very small, pale yellowish glands.

The terminal and axillary inflorescences are curved, erect spikes 40 – 50 cm long.
Flowers open from the bottom up with only a few open at any one time.
The flowers, around 10 mm across, come in shades of red and pink.

The flowers have no stalks being directly attached to the main axis of the spike.
The lower part of the flower is actually sunken into the main axis.
There are hairy green bracts at the base of each flower.
The bases of the 5 sepals are fused into a narrow calyx tube up to 14 mm long.
Five prominent green ridges on the calyx tube end in 0.5 mm long lobes on the rim.
There are hairs on the outer surface of the calyx.

The petal bases form a curved corolla tube up to 2 cm long.
On the rim are 5 spreading lobes.

The lobes are unequal and appears slightly bilabiate.
There are 2 lobes in the upper section or lip and 3 in the lower.
There are short hairs on the inner surface of the lobes and longer ones in the tube.
The flowers are shades or red and pink.

There are 4 stamens 2 of which are reduced to staminodes.
The filaments have white hairs with those on the staminodes being longer.
Each stamen has 2 anther sacs that lie vertically above each other.
The sacs open inwards via long slits.

The ovary of 2 fused carpels is superior with 2 locules each having 1 or 2 ovules.
The tip of the style, with a reddish stigma, curves up slightly.

The fruit are schizocarps 4 – 5 mm long.
They split into 2 indehiscent mericarps that each have 1 seed.