Monday, February 8, 2010

A Silky Haired Trio - The Petrocosmea sericea Group - I

In my continuing quest to know the genus Petrocosmea better, I've been focusing lately on a trio of plants that I call the "Sericea Group". Why do I call them this? Well, because these three plants are yet more of our wonderful Pet species which are currently victims of the identity crisis that plagues this genus. Only one currently has a species name attached and even that one may be incorrectly attached to this plant. That species, Petrocosmea sericea (pictured below) is the first of the group to come into cultivation in the USA, and this is the name applied to it from that time until today. So, I use that one,being the first and the only one with a species name, as the species around which I "lump" the other two plants...those being Petrocosmea sp. 'HT-2' and Petrocosmea sp. ? 'JR 2008-1'. These three plants are the focus of this short series.

So, what do I know about these three beautiful species? Well, the do all appear to be very closely related to each other....perhaps even three forms of the same species. The early DNA analysis does place them very closely related to each other, but three clear distinct individuals. In other word, they are not the same individuals...the DNA is a bit different, but they may be the same species. My personal opinion is that they are. Morphologically, they are very close also.

Secondly, they do appear to fit within the Section Anisochilus of the genus. Morpholically, the flower's anthers and corolla easily fit the defining characteristics to fit within that section. This section also includes the plants we currently grow as P. rosettifolia, and the P. minor (s). If you grow all of these, think about the flower structure and you can easily see that aside from size and color, the flowers are shaped almost identically in may respect. These all have the two upper petals that are shortened and bend forward, fused into a "hood" at the top of the flower. The flowers of the plants in the "Sericea group" all are nearly identical, with the only differences being that sp. 'HT-2' has a branced cyme with 1-5 flowers per cyme, while P. serciea most often has a single flower per cyme. I have not personally flowered the P. sp. ? 'JR 2008-1', but have seen photos of the flowers, which appear almost identical to the flowers of the other two species. All three plants have silvery hairs on the calyx lobes and cyme, making it appear silvery, frosted and silky.

Third, the leaves of all three species are similar, with the following differences. P. sericea has the most succulent leaves of the three plants, with the margins curled up forming a "spoon", which to my eye, is very attractive. The margins of the leaves of P. sp. 'HT-2' curl downward
in the opposite manner of the leaves of P. sericea, and are a bit smaller than the leaves of P. sericea, but are otherwise identical. The leaves of P. sp. ? 'JR2008-1' are the "thinnest" and softest of the three, and are clearly the largest of the group. They are softer to touch and more flexible. The "silkiest" if you will. This form also forms the most "open" rosette of the three plants. All three plants offset rarely for me, and tend to grow slowyly. The newest of the three.. sp. ? 'JR2008-1' grows the slowest of all. The plant pictured below is now nearly two years old and still is a small plant.

Petrocosmea sericea - the first of the group to come into cultivation around 2003. It is "close" to the published description of this species, although the published description mentions the hairs being golden or yellowish... the hairs on this plant are clearly silvery and "white". Otherwise the description is pretty close. I have to wonder if the description might have been written using dried or preserved plant material to describe, and perhaps the hairs turned more yellow or golden with age and drying? I have collected some leaves to press and dry in order to see if the colors of the hairs changes with age and drying.

The leaves of this plant cup upward and are the heaviest substance of the three...being quite succulent. This plant grows slowly, compared to all other species I grow, and makes a spectacular rosette as it ages. Two years, minimum, seems required to get a "mature" plant from a leaf propagation. The plant only gets better and flowers more heavily with age.
It also tolerates and seems to appreciate a bit of drying between watering and the leaves spoon more and look more silvery with higher light.

A comparison of two mature plants of P. sericea and P. sp. 'HT-2'...both of these plants are in 5" pan pots and are three years old when this photo was taken. They were grown side by side with identical culture to test the differences in the two species. Note that P. sericea, (left) is more silvery in appearance and the leaf margins cup upward forming a spoon. The leaves of P. sp. 'HT-2' (right) are greener in appearance and the margins are flat or curl downward. Leaf size is close, with the leaves of P. sp. 'HT-2' being a bit smaller on the average.

The newest species in the trio is one labeled P. sp. ? JR2008-1'. It came to me from a friend who got it from the collector in China in late 2008. This plant grows slowly. The plant in the photo above is two years old, and is still in a 3.5" pot. It has not yet flowered for me, but I have photos of the flowers which I will post in the next post on this group. The plant in all respects is very close to the other two morphologically. Leaves are much larger than the other two plants, even on this young plant. I currently have six smaller plants that were propped from this plant as "insurance" and to share with other Pet friends so that we can begin to get this form into broader cultivation. I am also sending a plant to a botanical garden as part of the collection there. It is always exciting to get new genetic material and new forms of Pet species in cultivation.

This photo shows the leaves of the three forms discussed in this post, for comparison. They are (Left to right): P. sericea (left), P. sp. 'HT-2' (middle) and P. sp. ? JR2008-1' (right).
These three plants add beautiful and interesting diversity to the family Petrocosmea in any collection. There is no other Pet that has the characteristics of these three. While P. nervosa and P. flaccida also have the silvery, silky hairs covering the leaves, the flowers of these are quite different. P. flaccida and P. nervosa have floral characteristics that place them within Section Petrocosmea of the family, while these plants clearly fit into Section Anisochilus. Additionally, the DNA data suggests that these three plants are very closely related to the group of P. minor(s). The"minors" are their closest relatives, according to the DNA. I have been successful in crossing P. sericea with P. minor veined leaf, when P. minor would not cross with other species. This willingness to hybridize with the minors suggests a close relationship also.
In the second installment on this topic, I will focus on the flowers of these three plants.