The clean, white flowers of Petrocosmea begoniifolia at are a lovely contrast to the dark green, purple-backed leaves that this plant bears. The purple of the leaves is carried into the pedicel and calyx, as can be seen here. The flower also has two lemon yellow splashes and has a more cup shaped corolla than most Pet species.Although white flowers in the genus Petrocosmea are among the minority, it occured to me this morning as I tended my beloved Pets that all of my white-flowered species are in flower now. I've always been partial to white flowers, any white flower...gardenias, magnolias, white roses....and the white flowered Pets are also among my favorites. So, I thought I would take advantage of natures gifts to post an entry about the white flowered Pets I grow.
Petrocosmea kerrii boasts white flowers with yellow highlights, much like P. begoniifolia, however, the yellow highlights on P. kerrii are uniquely on the top petals or "roof" of the throat, rather than the "floor" of the throat. Now, I have to see if I can cross P. kerrii with begoniifolia and get flowers with yellow on both the top and bottom petals??!!!It was interesting to me, to note that ALL white-flowered species have yellow in the flowers....something that is rarely ever noted in the blue flowered species. The yellow is usually found on the lower petals....with the exception of P. kerrii. P. kerrii is placed within Section Dienanthera of the genus, where a yellow blotch on the upper petals is a characteristic of the species within this section. (P. formosa, which has lavendar flowers is also placed within the Section, and it too, has yellow on the upper petals. ) By crossing the white-flowered species (with yellow in the lower petals) and the blue-flowered species (with no yellow in the flower), I have been able to get some yellow in purple flowers on the hybrids.
The Petrocosmea rosettifolia group (I have at least four different forms of P.rosettifolia), generally has lavendar flowers, with the exception of one form which I received labeled P. sp. 'G25KC00'. I have since labeled it P. rosettifolia #3. This form is the only one with white flowers. I used this form in my first hybrid - P. rosettifolia x sericea and got one white flowered seedling which also happened to be a miniature sized plant. I named that hybrid P. 'Keystone's Bantam'. All of the other seedlings from that cross have been lavendar, so far, however, I have about twenty more to flower this year, so I may still get some new white forms.
The white-flowered form of P. rosettifolia which I labeled #3 in my collection in order to identify it seperately from the other three forms that I have. This form also has three bracts on the cyme, and the flowers have a heavier substance and larger size than the other forms of the species that I grow. The cymes are also larger in diameter and grow taller. 
The dainty little charmer, P. barbata has flowers that almost always open white and stay white until the wither. For others, these same plants produce lavendar flowers, so P. barbata may not truly be "white flowered", and the trait may be cultural or environmental. It has the smallest and most fragile, thin flowers of any of the Pet species, for me. A heavy bloomer that is often among the very first species to bloom as Pet season approaches each autumn. One other thing of interest with this species is the fact that it tends to have a "semi-dormancy" after flowering where the outer leaves are dropped and only a tightly cupped center "button" of green leaves remains, until spring approaches, when the plant once again, springs into growth. 
Petrocosmea 'Keystone's Bantam'--- My only white-flowered seedling from among about forty seedlings that I have flowered, so far. The happy result from my first hybrid cross P. rosettifolia #3 x sericea. This seedling was tiny from the very beginning and has never exceeded three inches in diameter, even after three years of growth on the original plant. Flowers are large for the size of the plant, and are purest white, with NO yellow! The flowers on this seedling resemble the flowers of the rosettifolia parent, pictured above, most closely, while the flowers on all of it's siblings have favored the sericea parent more. The little plant originally had an "odd" center that resembled a little furry button, (note this in the photo above), however, the plant grew out of this and now this same plant has a "normal" center of tiny leaves. The plant above is in a two inch pot. Potting it into a larger pot did not result in a larger plant. Leaves are a little more reluctanct to produce babies than it's siblings, however, the plant does propagate true from leaves. It is quite floriferous at maturity and has been used once successfully in a hybrid with P. forrestii, which has produced 100% seedlings that are just as small or smaller than P. 'Keystone's Bantam'. I am awaiting the first flowering of these seedlings this winter. This is, I believe, the first and only hybrid Petrocosmea to date with white flowers.So, now that I am blessed with an assortment of white flowered Pets all flowering at the same time, you KNOW that I have to attempt some hybrids among them. P. kerrii might introduce more flowers into hybrids, since it's flowers are often borne in clusters of several flowers each. P. kerrii also has the potential to extend the yellow to the upper petals of the flowers, so in combination with another species with the yellow in the base of the flower, one might acheive flowers with yellow on all petals. P. rosettifolia #3 has a lovely yellow veining down the center of the dark leaves, so more attractive foliage might be possible with it as a parent. So, the potential is certainly there for some exciting new hybrids! Now, off I got to the plant room...........
