A new (old) cactus species for Pennsylvania.

The flower of Opuntia cespitosa. Notice the red-orange bases of the tepals, compared to the pure yellow flowers of O. humifusa.

A few weekends ago, I was messing around on Facebook, when a blog post by the New England Wildflower Society caught my eye. This article highlighted a split in of the eastern prickly pear cactus (Opuntia humifusa) into two species--O. humifusa and O. cespitosa.  I shared it with our botanist at work, and he agreed that it appeared to be a valid taxonomic split, supported by a variety of methods. It's interesting that O. cespitosa is an originally a name given by Rafinesque in the 1800s. Like, many of the species Rafinesque described, there was no type species available and, over time, the species was lumped into O. humifusa. The recent work that led to the resurrection of this species was done by Lucas Majure (papers linked from here).

Notice the long spines on the pads, this is one of the features that differentiated this species from Opuntia humifusa.

Looking around in the online herbarium databases (the benefits of digitized collections), we found a putative example of this species in Pennsylvania from an 1862 specimen along the Susquehanna River. Not being aware of any extant populations, we were planning on ending this to the Pennsylvania flora as an extirpated species.

However, I was up in Erie County working on vegetation plots, when we came across a small population of Opuntia that I had documented a few years previously. Back then, I had called it O. humifusa, as I wasn't aware of another taxon in the state at the time. However, this time the species was in flower, and it was obvious from that this was indeed O. cepitosa given the red-orange coloration of the flower and the long spines. This was a fairly exciting change in identity for this population of the species, especially as we now have a confirmed extant population of this species in Pennsylvania.