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Monday - June 22, 2015

From: Nederland, TX
Region: Southwest
Topic: Plant Identification
Title: Difference between Oxalis debilis and Oxalis violacea
Answered by: Nan Hampton

QUESTION:

There are two species of pink oxalis reported to grow here in Jefferson County, Oxalis debilis (introduced) and O. violacea (native). How can I positively identify which one I have growing in my yard?

ANSWER:

Oxalis violacea (Violet woodsorrel) is the native species and Oxalis debilis (Pink wood sorrel) is an escaped ornamental plant that is native to tropical America. Here is a description of O. debilis from PIER (Pacific Islands Ecosystems at Risk and here are descriptions of O. debilis var. corymbosa from Wildlife of Hawaii and from Q-Bank, a European database of invasive plants. Here is a description of O. violacea from Illinois Wildflowers and an extensive description from New England Plant Conservation Program.

Here are some comparisons of the two species using the PIER description for O. debilis and the New England Plant Conservation Program description for O. violacea.

Leaves:

O. debilis — 1.5-4.5 cm long, 2-6.5 cm wide

O. violacea — 0.6-1.3 cm long

Sepals:

O. debilis — oblong, 3.5-5 (-6) mm long

O. violacea — 4-7 mm long, glabrous, each with an orange gland at the apex

Petioles:

O. debilis — slender, flexuous, ascending, 10-25 cm long, more or less villous

O. violacea — 7-13 cm long and glabrous

Petals:

O. debilis — pinkish purple, spatulate, 11-20 mm long

O. violacea — purple to white, 1-2 cm long (10-20 mm long)

So, to summarize the most obvious differences:

The leaves of O. debilis are longer than those of O. violacea
The sepals of O. violacea have an orange gland at the tip; whereas, none is described for O. debiiis.
The petioles of O. debilis are longer than those of O. violacea and they are hairy; wheras, those of O. violacea are smooth.

Nonetheless, these two plants are very similar. There is definitely overlap in sepal size and petal length, but there is very little overlap in the sizes of the leaves and the length of the petioles of the two species. You might be able to use the smoothness or hairyness of the petioles along with their length and the presence or absence or orange glands at the tips of the sepals to separate the two species.