Take These Taiwanese, Please
Reprinted from the Azalea Chapter Newsletter
The Taiwan Venture in the early 1970s resulted in the widespread distribution of seed from some fascinating species from that part of the world. From these seed, I have been growing R. morii, nankotaisanense, pseudochrysanthum, and hyperythrum. Both morii and pseudochrysanthum of the Series Barbatum, Subseries Maculiferium, are rated to minus 10 degrees. Hyperythrum, of the Ponticum Series, Subseries Caucasicum, is rated to minus 15 degrees. All of these do well in North Georgia.
Until further testing can be done, nankotaisanense must be container-grown as its hardiness rating is still questionable. Experimenting continues by setting into the garden 6 to 8 year old plants in areas of various levels of protection from cold and wind.
Morii has 2 inch-long bell-shaped flowers, either pure white or blushed rose, heavily blotched with red. An interesting aspect of the foliage is that it maintains a symmetrical "collar" around the stem and truss. This species is more robust than either pseudochrysanthum or hyperythrum and makes a great addition to a species collection. There are two Patrick forms, one white, one pink, and of course the Windsor form is white.
Nankotaisanense is a rare species. Even though E.H. Wilson prophesied in 1918 where it could be found, Taiwan Venture Director Dr. Chien-Hsu only located it in the 1970s - some 10,000 feet up Mt. Nankotaisan on Taiwan. Nankotaisanense has smooth dark green leaves, with the underside a paler green, and has pink to white flowers. It is believed to be closely related to pseudochrysanthum.
Pseudochrysanthum in all its variable forms is indeed the choice species so far from Taiwan. Leaves are ovate, elliptic or oblong-lanceolate, glossy dark green on top, the underside paler, and both sides slightly hairy. The surprisingly large truss opens from dark pink buds and ages pale pink to white. The flower's bud-to-last-stage-of-bloom metamorphosis gives the joyful effect of being three plants in one - the stunning two-toned first stage, the smooth pale pink fully opened truss second stage, and the all white mature last stage.
Pseudochrysanthum is a rather slow growing and slow blooming plant, taking 6 to 10 years to develop a significant showing of either. But it is most rewarding to those who wait. Fortunately I got a head start years ago by purchasing both the Exbury and Ben Nelson forms as 10 to 12 inch plants. The Ben Nelson form has longer, larger leaves, with indumentum along the midvein on the undersides and silvery tomentum dusting the leaves and stems of new growth. The Exbury form, an award of merit plant, is known as the great silver foliage form.
One population of pseudochrysanthum, located at the summit of Mt. Morrison on Taiwan, appears to be an ecological dwarf. It is totally isolated from any other rhododendron. One plant 12 inches high was estimated to be 35 years old. This estimate was established by counting growth rings allowing 1 mm diameter of growth per year.
Seed were collected during the Taiwan Venture and planted by some west coast growers. I know some dwarf plants are being offered for sale by a west coast nursery, but I do not know whether these have been grown from seed or from cuttings. It was questionable at the time whether plants grown from these seed would remain dwarf or attain the size of the Exbury form. Any form of this delightful species is welcome in my garden.
Hyperythrum has lovely white flowers that open from pink buds. The truss is surprisingly large coming from rather small buds. With its long, narrow curled leaves creating remarkable interest year round, this is a desirable foliage plant for the garden even if it never blooms.
Even though E.H. Wilson searched the Island of Taiwan in the early 1900s and sent hyperythrum seed to Arnold Arboretum, general distribution was not made until after the Venture. Dr. Hsu located a population of hyperythrum at quite low elevation near Taipei which should prove useful in developing heat tolerant hybrids.
There are several forms of hyperythrum available such as Windsor, Sunningdale, and Patrick. But in the spring, the focal point of interest in my garden is the site where a dozen bronze-leaf hyperythrum show off their brilliant and colorful new foliage of variable leaf size and shape. These plants are too young to bloom, but who cares. One can stand only so much sweep of beauty.
After the minus-12 degree weather of January 1985, these plants lost all their leaves. To my amazement, during the spring, all except one put on new leaves and today they show no signs of winter damage. Love those Taiwanese!