Bletilla striata (Thunberg) Reichenbach f. (Family Orchidaceae) is one of the wonderful surprises that you may encounter in flower this spring at MEMBG. This is a species of terrestrial orchids originating from southern Japan and China. In Japan the species is called shi-ran, meaning purple orchid. In China it's known as pai chi. But popular gardening references have named this plant the Chinese ground orchid.
Bletilla, as you might imagine, is a diminutive of Bletia, a New World genus of terrestrial orchids to which certain species of Bletilla bear a resemblance. The specific epithet refers to the plicate (shallowly pleated) leaves, which are striate (marked with parallel bands or lines) and have light-colored veins alternating with green tissue. Striate could also be used to describe the variegated leaves of certain cultivars that have alternating strips of white and green. Our clone, growing best near the gymnosperms at the end of the recirculating stream, occasionally possesses a thin white strip along the leaf margin.
Shi-ran is an orchid species that generally has four to six leaves per shoot and grows to less than fifty centimeters tall. Each leaf has a basal portion, the leaf sheath, that encircles the one-centimeter-thick stem. The first leaf of each shoot never forms a recognizable leaf blade, and the second leaf has a small elliptic blade. On our plants, the dominant leaf form is oblong-lanceolate with an acuminate (pointed) tip. Typically, this blade may grow to twenty or thirty centimeters in length and up to 5.5 centimeters wide. Leaf arrangement is alternate distichous (arranged in two vertical rows). Arising from the shoot apex is an unbranched terminal inflorescence of six to ten (or twelve) flowers, a spike-like raceme with essentially no pedicels on which the lowest flower is the oldest and the uppermost the youngest.
The shoot of B. striata is determinate, living for only one growing season and then dying back to ground level. Some books refer to this type of orchid as a deciduous orchid, but a more accurate term would be herbaceous perennial or geophyte. Geophyte in particular would be a good descriptor of B. striata, because it grows via short rhizomes from which it forms a larger, white, horizontally compressed corm (a pseudobulb). Fibrous adventitious roots arise from all sides of the corm, along with new shoots that are connected by the short, cylindrical rhizomes.
Anybody familiar with corsage orchids would have no difficulty recognizing that Bletilla is also an orchid, even though its flowers are less than five centimeters across. Flowers are lax, somewhat nodding, and resupinate (twisted somewhat from horizontal). On our clone, the three sepals and two unmodified petals are colored red-magenta (red-violet; originating from cyanidin-type anthocyanin pigments) and are all fairly similar in form, whereas the third petal, the lip (also called the labellum), when viewed from the side looks like a light-lavender luge with three violet lobes. Inside this highly modified petal, the floor of the lip bears five parallel, frilled white ridges. Important sexual parts of the flower--the style with two stigma lobes and one anther--form a column that overarches the lip.
Orchids have intricate mechanisms for pollination. An animal visitor is needed to transport pollen from the anther of one flower to a stigma lobe of the next. Pollen grains in Orchidaceae are not separate but instead form a large mass, called a pollinium, that must be deposited on a receptive stigma. Bletilla striata has four pollinia per anther, and in this genus the pollinia are described as being soft and mealy, unlike the hard pollinia found in most genera. Its lightly scented flowers are likely pollinated by bees, and outdoor plants at MEMBG set some fruits.
Orchids require many pollen grains to be transported at once because the inferior ovary contains thousands of ovules to be fertilized. Each fertilized ovule becomes a seed, here barely larger than a speck of dust. In fact, orchids were once called the Microspermae, because they have so-called "micro seeds." So small are these seeds that the embryo also is incredibly tiny. Typically, orchids do not even have a cotyledon on the embryo; neither do they form a radicle (root) or leaves. Thus, when the fruit, a capsule dries and splits open, the incredibly light seeds of this family can be carried long distances by the wind. For an orchid seed to germinate and become established, a helpful mycorrhizal fungus must infect the embryo, invading cells and assisting the plant in absorbing nutrients.
Bletilla striata is of especial interest in having an embryo with a rudimentary, vascularized cotyledon--it is one of only ten species (among more than 22,000 orchid species) that does! Moreover, most orchids totally lack endosperm next to the embryo, but in Bletilla some endospermal cells persist within the seed. Bletilla striata also has an interesting capsule that splits open along six lines of weakness.
Bletilla is a genus of nine or ten species that tend to grow well in partial shade, as in a woodland setting, and prosper in warm temperate climates. Actually, most of the world's orchid species occur in the wet tropics, and nearly two-thirds of the known species are epiphytes in wet tropical forests. But in both warm temperate and tropical locations this terrestrial orchid, B. striata, has been cultivated as a medicinal plant. In Vietnam, for example, ts corm (pseudobulb) is used to treat tuberculosis and other pulmonary diseases, as well as to relieve pain from burns. An unknown ingredient in the corm promotes clotting of the blood.
ARTHUR C. GIBSON, MEMBG Director