Tuesday, March 16, 2010

Petrocosmea flaccida - Part I - An Overview

In this new series of posts, I decided to focus on a species that for many of us was the first Petrocosmea we grew, Petrocosmea flaccida. I want to include an overview of the species and it's history, characteristics, varieties or clones available in cultivation, it's culture, and finally it's influence upon it's several hybrids.

The photo above, taken by my friend Julie Mavity-Hudson, illustrates the obvious ornamental qualities of this species. The charming deep violet-purple flowers, which are perhaps the darkest of any Petrocosmea species in cultivation, crowing the silvery, flaccid gray-green leaves.
The photo above was taken by Ben Paternoster of his beautiful, expertly grown P. flaccida in a five inch pan pot. He sent this photo to me a few months after he had potted the plant in a shallow 5" pan pot, following a discussion where I advocated using shallow pan pots for the culture of Petrocosmea. Ben's skill as an expert grower likely contributed to this magnificent specimen much more than the pan pot did. This specimen was grown in his basement, under lights, in Long Island, NY. A beautiful example of the results possible with this species.
Petrocosmea flaccida was initially discovered in Southwestern Sichuan, northwestern Yunnan, China growing on rocks, in thickets at between 1830 and 3000 meters above sea level. Described by Craib in 1919, it is placed in Section : Petrocosmea. This section contains species considered to be among the most primitive species of the genus, based on the reproductive structures. The upper and lower corolla lobes are roughly the same length. Anthers are seperated on either side of the ovary. Flower color is deep violet purple, with small white "fang like" marks at the base of the upper and lower petals. The peduncles are thin and wiry, sometimes with a purple hue, and single flowered. The pistil of this species is also dark purple in color as opposed to the white color of most Pet pistils.
The leaves of the species are pale gray-green, covered in silvery hairs and are flaccid, hence the name. The rosette of this species tends to be very flat, and on a large plant, outer rosette leaves will droop, due to the weak petioles. After flowering, the outer leaves will tend to yellow and die off, leaving a very tight, silvery green center of new growth which tends to sit in "suspended animation" until warmer weather when a growth spurt will occur. Often, the plant will form offsets after flowering also.

Petrocosmea flaccida's flowers are among the darkest colored of any Petrocosmea species. The upper petals tend to stand upright, and the rouned shape reminds me of Mickey Mouse ears.

For many years, there was only one clone of P. flaccida in cultivation. Recently, a new collection from the Atlanta Botanic Garden has brought a new clone into our collections. The older "traditional" clone is pictured on the left, with the smaller, ABG clone on the right. The plants in this photo are of the same age and are growing in the same size pot, having been grown side by side on my light stands to test whether the new ABG clone was smaller due to culture or genetics. It remains noticeably smaller than the "traditional" clone, and thankfully, does not produce offsets as readily. Flowers of the smaller, ABG clone have less white in the base of the petals also. Flowers are about 1/3 smaller than those of the "traditional" clone. I have crossed these two clones and got very few seeds, with two seedlings that germinated. The seedlings remain too small at this point to comment on them.

The new P. flaccida clone from the Atlanta Botanic Garden remains quite small. Shown here in a three inch pot, it appears "over potted". I am hopeful that it will prove useful in producing miniature Petrocosmea hybrids.

Culture of P. flaccida is pretty much as it is for all my other Petrocosmea. I give it a cold and dry winter rest. New growth resumes in spring with longer days and warmer weather, when I increase watering and fertilizer. Both clones propagate easily from leaf cuttings. This species is on of the "deciduous" Pets...(a term I have begun using to describe those species that tend to loose outer leaves after flowering and seem to want a drier, colder rest. A central crown of small, tight, very hard new leaves develops and remains in "suspended animation", doing nothing until the warmer weather of spring, when new growth comes on rapidly. ) This trait is also seem in may of the hybrids with P. flaccida parentage.