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Vol. 8(8), pp. 9-12The McAllen International Orchid Society JournalAugust 2007

Stanhopea oculata and the Range of a Genus

R J Ferry

Fig. 1. Pl #290496-5, C-6. Stanhopea oculata (Lodd.) Lindl., Gen. Sp. Orchid. Pl.: 158. 1832. Digital photo: DSC_1757a, Monday, 30 July, 2007.

In sharp contrast to the long-lasting flowers of T. carthagenense, many of the well-known and commercially available hybrids of Phalaenopsis and other orchids, the flowers of the genus Stanhopea are complex, but tend to be very ephemeral. One plant used in your editor's doctoral research, Stanhopea oculata, popped open seven colorful and fragrant flowers on Monday, 30 July (Fig. 1). Only three days later, they're beginning to fade. The genus is known from South America, throughout the Meso-Americas, and well into Mexico. In fact, one species, S. maculata, is known from northwestern Mexico, at a latitude a little farther north than that of San Antonio, Texas!

Fig. 2. Inflorescence out, buds still close-in. Dig. photo DSC_1737a, Thurs., 26 July, 2007.

The plants are best cultured on either a mount or in a loosely woven (but very sturdy!) wire basket. Grown well, a plant can have a few dozen pseudobulbs and be big and heavy, so they're not plants to be cultured by the faint hearted! The vegetation tends to grow upward and have very large plicate leaves, although in an old, well-established specimen plant, one may see leaves protruding from the top, sides, and even the bottom of the basket. For most members, the flowering shoot begins from the base of the pseudobulb, and burrows outside the basket as a shoot, then grows downward for some distance before the flower buds really begin to enlarge (Fig. 2). There may be from two to several buds, depending on the species.

Fig. 3. Flower buds spreading apart. Digital photo DSC_1742a, Fri., 27 July, 2007.

Once the buds are out and hanging, they enlarge and when about to flower, separate from each other (Fig. 3). When ready, they usually all pop open at about the same time. Once open, the petals curve back; out of the way of the column and labellum.

For its part, the labellum is modified into a mesochile and hypochile. At the base of the labellum are osmophores, fragrance producing glands desighned to attract the male bees, usually members of the genus Euglossa. These bees look to gather fragrance to make themselves more attractive to the female bees. Obviously the male gathering the most fragrance is more attractive, and hence natural selection favors the strongest bee to be likely at gathering the most fragrance, and also the most successful at reproducing. Flowers tend to last only a few days, but while they last, they're spectacular and unusual! Attracted by the fragrance located basally, the bee scratches vigorously until fatigued or drunk on the fragrance, and falls, sliding down the mesochile and guided by the horns of the hypochile right past the near-end of the column. At this point, brushing past the column, the flower places its pollen on the bee's thorax. Our drunken bee falls to the ground, and as he recovers, the stipes, the pollen's "stalk," dries quickly and bends the pollinia backwards so that the next time the bee falls through a flower, the pollen gets neatly deposited in the right place for fertilizing the flower! It's a win-win situation: the bee gets the needed fragrance, and the flower is fertilized; probably cross-fertilized from another plant!

Fig. 4. Individual flower, fully open. Note 90° bend in mesochile of labellum. Digital photo DSC_1759a Monday, 30 July, 2007.

There are several euglossine bee species, and some stanhopeas are pollinator-specific with only one species of the correct size to fit in and fall through the flower's pollinating trap. Others may accommodate two or even three bee species as pollinators. S. oculata is particularly interesting, because its labellum, the mesochile (the section with the two dark spots) has a sharp, 90° bend in it (Fig. 4). This bend allows no less than six different bee species to pollinate it. As a result, S. oculata is the one species of the genus found from Colombia throughout the Meso-Americas and clear into Mexico! In contrast, S. reichenbachia, the most primitive species of the genus, known only from Colombia, allows only one bee species. The same is the case with S. intermedia, the most evolutionarily advanced (recent) of the genus, known only from Mexico.

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In researching this genus, your editor made leaf-prints of the upper (adaxial; haz) and lower (abaxial; envéz) surfaces of leaves of Stanhopea species. Leaf cells were then randomly selected and individual areas measured. When a certain number of measured cells had been measured, these areas were totaled and their means (averages) and standard deviations was computed. Given the spreadsheet made up by the computer genius, Dr. Eric Olsen, one could display these data in tabular form or the data could be displayed as the normal (Gaussian) curve of the species. Going further, Dr. Olsen supplied your editor with the ability to display the curve-data from multiple different species in a single display! Thus the curve-data of a few species could be graphically readily compared with each other.

Fig. 5. Gaussian curves. C-51 S. reichenbachia, C05 & C06 S. oculata, and C51 S. intermedia. Figure from Appendix A-II, page 9 of doctoral dissertation, R. J. Ferry, 1999

The adaxial cell data (Fig. 5) of the primitive (C-21 S. reichenbachia, the yellow curve), the most evolutionarily advanced or recent (C-51 S. intermedia), and two specimens of S. oculata (C-5, the green curve, and C-6, the blue curve, and one shown in flower in this issue) offers some interesting data.

1. C-21. S. reichenbachia, the most primitive species of the genus, has the largest cells, with an area average of 5623.69µ.

2. C. 51 S. intermedia, the most evolutionarily advanced member of the genus, has the smallest cells, with an area average of 2673.67µ.

3. Of the two S. oculata specimens shown, C-05 has 4123.24µ, and C06 has 4173.52µ.

Totaling the areas from the most primitive species and most advanced species yields 8297.36, and dividing that number by 2 = 4148.68µ. The areas of the S. oculata specimens total 8296.76µ, and dividing that number by 2 = 4148.38µ, is very close to the average of the extremes, and well within the statistical parameter of ρ = .05. In other words, because of its acclimation to the full range of pollinators, S. oculata has evolved to be an intermediate species between the most primitive and most advanced members of the genus!

As expected, the bee-pollinators of S. reichenbachia and S. intermedia differ greatly in size and geography. Your editor is unaware of any research to compare pollinators as he did with the plants, but one suspects the results would provide another example of the co-evolution of flowers and insects.

Copyright © 2007 R J Ferry