ID: Colocasia vs Xanthosoma vs Alocasia
In Texas, about 90% of the wild iNaturalist observations of Araceae are Colocasia esculenta, and about 8% are Xanthosoma sagittifolium.
Colocasia leaves reach a height of about 3', and are generally heart shaped with the petiole (leaf stem) attaching to the back side of the leaf. There is often (but not always) a light purple colored dot on the front of the leaf where the petiole attaches. The far edge of the leaf (tip of the heart shape) hangs downward (except in very young leaves).
There are multiple Colocasia species sold ornamentally, but only Colocasia esculenta seems to thrive when it escapes into the wild in Texas.
Xanthosoma leaves can reach a height of about 9' tall, and are generally arrowhead shaped with the leaf stem attaching at the edge of the leaf in the notch of the arrow. The tip of the arrowhead shape hangs downward (except in young leaves).
Xanthosoma sagittifolium is the only species documented to thrive when it escapes into Texas. This species seems best confirmed from photos that show the notch where the petiole attaches - this species has leaf margins that extend almost completely to the edge of the notch.
Xanthosoma robustum has been documented from a few sites in Texas, mostly ornamental gardens. It has leaf margins that end about 1.5-2.0 cm from the posterior rib at the base (the V shaped ribs are "naked" for about one inch).
Alocasia has large leaves like Xanthosoma but the leaves typically point upward even when mature. Observations of this species from Texas seem to mostly be non-wild, potted plants.
A quick visual of the differences between elephant ear genera can be found at
https://durablegardening.blogspot.com/2011/01/whats-difference-alocasia-colocasia-and.html
The best reference for distribution and identification of Colocasia, Xanthosoma, and Alocasia in the southeastern US is Serviss et al., 2000, which can be found online at
https://www.jstor.org/stable/41967766
For details of Xanthosoma ID, see Croat et al., 2017, at
https://adoptabosque.org/wp-content/uploads/2020/09/XanthosomaAraceae.pdf
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Great straightforward write-up for those of us not familiar with elephant ears (which put the "common" in "common name"!). Thank you!
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