Commelina diffusa (COMMELINACEAE) Blue Commelina

A weak-stemmed creeping herb producing short upright branches and rooting at the joints (nodes) of the stem. Native to Australia, tropical Asia and Polynesia. Although native, often considered a weed of damp or shady places, gardens and along watercourses. This is because it behaves weedily, occupying areas where clearing has led to an excess of sunlight. It is not a problem in normally shaded creek banks with deep leaf litter, especially Casuarina spp. Other Commelina species such as C. benghalensis are not local so it is important to learn the differences. See the Weeds to Whack section. Stems are soft and creep along the ground, often producing short upright branches. The leaves have an obvious leaf sheath which can sometimes be hairy (pubescent) but never with brown hairs a characteristic of C. benghalensis. Leaf blades either elongated or egg-shaped (ovate). They are generally hairless (glabrous) and come to a sharp point (apex acute).

Flowers are bright blue with three petals and three yellow stamens. Flowering occurs during spring, summer and especially during autumn. The fruit (capsules) are about 5 mm long.

This picture shows both the hairy sheath at the base of the leaf clasping the stem and also the base of the spathe (leafy structure at the base of the inflorescence) which is not fused and does not hide the flower stalk. The spathe of the exotic weed C. benghalensis is funnel shaped and fused (encloses the flower stalk).

The blue flowers of this plant occasionally attract the Blue-banded Bee, an insect which sees best in the blue range, and is therefore attracted to blue flowers.