Tuesday, September 15, 2009

Petrocosmea nervosa and sp. 'vittatae' - Are they the same species?

Petrocosmea sp. 'vittatae', sometime distributed as P. vittatae, is obviously a close relative, if not the same species as P. nervosa. P. vittatae is not a valid species name.

I have always had a special fondness for Petrocomea nervosa. It was one of the earliest Pets that I learned to grow and it never fails to bloom faithfully and heavily for me every year. The grey, silvery hairy foliage crowned with a mass of blue flowers never fails to make me feel happy when I look at it. My three plants of P. nervosa are all putting on their best show for me right now.

One of my happy P. nervosa plants in bloom today. Notice the offsets near the center crown.

Petrocosmea nervosa flower.
The upper petals being nearly the same length as the three lower petals is one of the characteristics that places P. nervosa within Section Petrocosmea of the genus Petrocosmea. This section is believed by some taxonomists to contain the most primitive species within the genus based on flower structure and the configuration of the anthers. As morphologically similar plant labeled P. vittatae was introduced into cultivation a few years ago. The late Maryjane Evans spent much effort researching the origins of the new plant material as well as the name P. vittatae and found nothing. The person who gave the plant to her could not recall from whom they had originally gotten the plant, and the species P. vittatae is not a valid published species within the genus. I have noted that P. sp. 'vittatae' grows larger and has leaves of heavier substance, and substantially larger in size than P. nervosa, when grown side by side with uniform culture. Both plants offset heavily as they approach maturity and tend to only flower once they have produced offsets. The flowers of both plants are identical in every way for me in my conditions and the plants bloom at the same time. If shown a leaf, though, I can usually tell which leaf is 'vittatae' and which is nervosa, due to the larger size and thicker, heavier substance. I find that sp. 'vittatae' matures a little faster than nervosa in my conditions and tends to produce plantlets from leaf cuttings faster than nervosa.

P. sp. 'vittatae' on the left and P. nervosa on the right. Both of these plants were grown side by side in the same tray on my light stands and were taken from leaf cuttings put down to root on the same day. They are shown in five inch pan pots.

P. sp. 'vittatae' growing on my lightstand. From this photo, one can see that I grow this species with quite dim artificial light. Note the offsets...this species and P. nervosa bloom for me only once they have produced offsets.
I grow both species in quite dim light. SHALLOW pots...a must!, an I keep soil evenly moist with occasional short periods where I allow it to dry a bit. I find that these species are a bit more succulent than some others and prefer soil a bit drier. Once potted in a five inch pan pot, I leave them there for several years as long as they are happy and healthy. I find that they bloom most heavily when not disturbed and allowed to mature and get a bit rootbound. I remove a thin layer of soil once a year and replace it with fresh medium containing systemic pestacide granules. I have never been troubled with insects with this treatment and my plants seem happy.
SO, what do you do if you have P. vittatae? First, keep it if you like it. A few years ago, once it was announced that research had found no such species as P. vittatae, some experienced Pet purists were saying that any plant labeled "P. vittatae" should be thrown away and NOT distributed as there was "no P. vittatae". My feeling is that it IS a Petrocosmea, and it IS a slightly different plant than P. nervosa...so we should continue to grow it and keep the plant labeled as something new and different. I changed my labeling from P. vittatae to P. species 'vittatae'...in order to designate that it is a species that is unidentified and was given a cultivar name of 'vittatae'. Whether that is right or wrong, it allows me to keep it seperately labeled in my collection and it continues to adorn my home and enrich my life with it's beauty....regardless of it's name. You know....."A rose by any other name.........."