Sunday, September 13, 2009

An Overview of Petrocosmea - To Know Them Is To Love Them

One of my favorite Chinese proverbs states that when someone shares something of value with us, we have an obligation to pass it on to someone else. I think that sums up my reason for starting this blog....

When my interest in knowing more about Petrocosmea first began, I found it extremely difficult to find information about the genus, and even more difficult to find information on proper culture of the plants. It is my hope, that in writing about what I have learned, and continue to learn about the genus as I continue to study it, that others who want to know more and grow Petrocosmea more successfully will find the information helpful.

So, I thought with this post, I would review the genus as a whole.

The genus Petrocosmea was first described in 1887 from Dr. Augustin Henry's Ichang collections by Daniel Oliver when he described the species P. sinensis from western Hubei, which is a province in central China, near the Yangtze River. In 1919, William Craib wrote the First Revision of the Genus Petrocosmea. No further revisions were done until Wang Wencai did the Second Revision in 1985. The genus includes three sections: Section Petrocosmea, Section Anisochilus, and Section Dienanthera. Among the three sections, the total described species in the 1985 revision is 27 known species and 4 varieties. A 28th species...P. formosa, was described by B.L. Burtt in 1998. The name Petrocosmea comes from the Greek words for "pretty" and "rock". The chromosome count for Petrocosmea is 34.

The geographical distribution of the 28 species contained in the genus includes 24 species and 4 varieties from Western and Central China, with the remainder found in Myanmar (Burma), Thailand, NE India and S. Vietnam. The species are often found in very restricted locations, in forests, growing among limestone rocks at elevations from 300 - 3200 meters. This elevation is typically cool to rather cold in temperature. Humidity is generally high due to mists at these elevations, and the locations are often near streams. The species are often found on only one or two mountain tops or on one or two islands.

The center of the rosette of P. sericea. I really like the cupping of the leaves on this furry species! It is one of the slowest growers of the genus, at least in my conditions.
The first Section described was Section Petrocosmea, which includes the species considered to be the most primitive of the genus. This section of genus contains seven species and one variety. One of the distinguishing features of the species in this section is that the upper lip of the corolla is nearly equal to the lower lip of the corolla. It contains the species P. flaccida, P. nervosa, and P. grandiflora. Examine the flowers of these species, and it will be apparent that the upper petals and the lower petals are very nearly the same length.

The flower of P. duclouxii, which I suspect may actually be P. grandiflora. This plant has also been distributed as P. floribunda, a species name that is invalid.
The second Section described is Section Anisochilus, the largest section, containing 16 species and two varieties. P. parryorum is a commonly grown species found within this section. One distinguishing feature of the species within this section is that the corolla upper lip is half the length of the lower lip. This section also includes P. barbata, P. rosettifolia, and P. forrestii

The flower of P. rosettifolia #1.

The foliage of P. rosettifolia #3. The lovely yellow veining along the central and lateral veins is passed along in hybridizing to the progeny....something I was happy to discover!

The third section within the genus is the last to be described, being added by Wang during his revision of the genus in 1985..Section Dienanthera. The flowers of this section have a uniquely different pollination mechanism from the other two sections. The anthers are constricted below the apex to form a short "beak" that actually ejects the pollen from the tip of the beak when pressure is applied to the base of the beak. P. formosa is a species found within this section along with P. kerrii. The species within this section often have a rather large leaf blades with longer peduncles.
So, as your Pets come into flower this season. Take the time to examine the individual flowers up close. I have learned a lot about the genus by examining the flowers. I am often asked if I know the natural pollinators of Petrocosmea. I do not. I have been unable to find any information or even speculation on how the flowers are pollinated in nature. If anyone know, please let me know!