Saprophytic Orchids of Dallas

IN THE SUMMER of 1981, I was wandering around the escarpment of southwest Dallas, Texas, in search of something photogenic to put on the last half of a roll of film so I could send it off to be developed. My wanderings brought me to a grove of junipers and oaks. After looking around for a while, I noticed something that looked at first glance like an orchid. I did not know there were any orchids in the Dallas area, so I was quite surprised. On closer inspection, it was clear that I was looking at the stem of an orchid plant laden with seed capsules. There were no leaves or open flowers on the plant. I looked around for others but found none except a smaller plant growing right beside the first one. When I got home, I looked through one of my orchid books and concluded that what I had found was probably a species of Corallorhiza.

In August of 1982, I went back to the same place to see if the plant had come up again. Unfortunately, it had not. So I looked around the immediate area for other plants. It was not long before I found about a dozen plants full of flower buds and developing ovaries. Only one plant had an open flower, and that flower was open only partially. I looked through several orchid books to try to identify the orchid, but I could not find any matches. Any plant that looked remotely like the right species had a range that did not include the Dallas area.

The following year, I started sooner in my search for the plants in order to catch them in an earlier stage of development. However, instead of finding immature inflorescences of the same species, I found another species in full bloom. I sent a specimen to the Orchid Identification Center at the Marie Selby Botanical Gardens in Sarasota, Florida, and the plant was identified as Corallorhiza wisteriana, a fairly widespread species whose range includes the Dallas area.

The plants I originally was looking for did not come up that year at all. It wasn't until July of 1986 that they came up again. This time, I dissected one of the flowers to try to make a proper identification. I noticed that instead of having four pollinia, as corallorhizas do, it had eight. By that time, I was somewhat familiar with the genus Hexalectris, so I concluded that the plant was a species of that genus. The size and shape of the flowers when spread out flat indicated that the plant was Hexalectris nitida. However, the range was wrong. Hexalectris nitida had been reported only in Panther Hill in the Glass Mountains of Brewster County, Texas, and in the Sierra Mojada in the state of Coahuila, Mexico. There were some other problems. In Carlyle A. Luer's The Native Orchids of the United States and Canada Excluding Florida, Hexalectris nitida was described as having open flowers with sepals and petals curving backward toward the stem. The plants in Dallas very rarely had open flowers. Another difference was that according to Luer, there were five ridges on the tip of the lip's mid-lobe. The plants in Dallas had five ridges on the lip, but the ridges were not at the tip. Because of the differences, I sent a specimen to the O.I.C. for identification. Soon I got a reply confirming that the plant was an autogamous form of Hexalectris nitida.

In Dallas, Hexalectris nitida seems to prefer living in the leaf litter of a mixed juniper and oak forest. Although I have seen some plants in oak litter, the vast majority prefer a bed of decaying juniper needles below which is limestone bedrock. Although all the plants seen were growing near the escarpment, they did not grow past the edge. Presumably, this is because moisture cannot accumulate very well on the sloped surfaces of the escarpment. Also, the soil is not as thick on the slanted surfaces.

Corallorhiza wisteriana grows in the smae forest as Hexalectris nitida. However, Corallorhiza wisteriana prefers forest dominated by oaks, whereas Hexalectris nitida prefers junipers. Corallorhiza wisteriana also grows in poorer, sandy soil that is populated by grasses. Plants growing in these areas were always smaller than the ones growing in oak litter. Corallorhiza wisteriana also seems more tolerant of sunlight. Plants frequently are seen in clearings in the forest.

Another saprophytic species previously unknown in this area is Hexalectris warnockii. When I found the original plant of Hexalectris nitida in 1981, I told Dale Williams, an orchid grower who lived near the location of the orchids. I asked him if he had ever seen any native orchids in the area, and he said that he had not. My discovery piqued his curiosity, and after he saw the plant that I found, he kept his eye out for orchids in a neighboring property that was downwind from the plant that was blooming. In the summer of 1986, he was rewarded not only with many plants of Hexalectris nitida but also with a new, showy species, Hexalectris warnockii. This species was known to have occurred in parts of central Texas as well as the Big Bend area in Brewster County. Thus, Williams' discovery constitutes an extensionof the previous range.

Another saprophytic species reported in the area in 1986 is Hexalectris spicata. Although I have not seen any plants myself [since the article was published in the bulletin, I have seen many, including the one pictured], they have been seen at the Fort Worth Nature Center in Fort Worth, Texas.

As far as I can determine, nobody knows for sure what prompts these saprophytic species to bloom. One year they may have hundreds of flowers and the next year none. Therefore, I have accumulated weather data for the years 1980-1986 in an attempt to correlate blooming with temperature and rainfall. From this information, it seems clear that generous rainfall in the late spring is necessary for flowering of Hexalectris nitida. Similarly, early spring rains are required for the blooming of Corallorhiza wisteriana. This corresponds nicely to the blooming times of March to May for Corallorhiza wisteriana and July to September for Hexalectris nitida. I have not yet established a correlation with the temperature.