Native & exotic Commelinas

Native or exotic Commelinas.

The introduced Commelina benghalensis is easy to identify with the reddish-brown (rarely white) hairs on the top
    of the leaf sheath, flowers with a very small lower or anterior petal and 2 blue anthers.
Native species always have white hairs on the top of the sheath and the lower petal is almost as large as the upper two.

I find the native species in Queensland confusing especially with the correct names being uncertain.
The Australian Plant Name Index, the Australian Plant Census, The Plant list and World Flora Online for Commelina cyanea,
    C. diffusa and C. lanceolata have the following.

  • Commelina cyanea is an accepted name with Commelina communis a synonym.
  • Commelina cyanea – misapplication Commelina diffusa.
  • Commelina cyanea is a misapplied name of Commelina lanceolata.
  • Commelina diffusa Synonym Commelina cyanea.
  • Commelina lanceolata – this name is not current and has been misapplied against the current name Commelina ciliata.
  • Commelina ciliata synonym Commelina acuminata and misapplication to Commelina lanceolata.

Commelina cyanea, C. diffusa and C. lanceolata are all seen as accepted species in various sources.

Some say C. cyanea and C. diffusa are the same while others say they are separate species.

One of the distinguishing features used is the leaf size but there is a large overlap between the species.
Leaf lengths in cms for C. cyanea 2 to 7 (10), C. diffusa 2 to 15 and C. lanceolata up to 12.
Leaf width in mms for C. cyanea up to 15 (20), C. diffusa 0.5 to 33 and C. lanceolate under 15.

Descriptions of C. diffusa say:
“centre-most stamen has a broad transverse band of violet” implying the violet band is always present
    while “medial stamen anther connective usually with transverse band of violet” indicates it is not always present.

I have plants I think are C. diffusa/cyanea but none have a definite violet connective.

In the following I have treated C. cyanea as a synonym of C. diffusa which is the older name.