SelbY!ln!l 7: 129-247 THE RELATIONSHIPS OF THE SLIPPER ORCHIDS (SUBFAMILY CYPRIPEDIOIDEAE, ORCHIDACEAE) John T. A twood, Jr. * ABSTRACT The phylogenetic relationships of the Cypripedioideae are adumbrated by the Wagner Groundplan-divergence method. The mutual resemblance be­ tween paleotropical Paphiopedilum and neotropicalPhragmipedium is doubt­ fully superficial since both share several derived vegetative character states and similar floral bud development. For these genera a simplified classifi­ cation is proposed, and one new taxonomic combination is provided. Selenipedium grades into Cypripedium via C. irapeanum and C. caUtor­ nicum. The correlation of reduced vegetative features with increasing lati­ tude suggests that temperate climates have altered the northern taxa most. By eliminating these features from cladistic analysis, C. arietinum (for which the genus Criosanthes is recommended) is parsimoniously distinct from the 3e/enipedium-Cypripedium clade. Similar flowers of Phragmipedium schlimii and Paphiopedilum subgenus Brachypetalum relate to neoteny, since the floral parts resemble those of young flower buds of related species. Their superficial floral similarity is in­ terpreted as a convergence. Chromosome numbers are reported for five species of Phragmipedium and nine species of Paphiopedilum. Since the basal chromosome number is interpreted as 2n = 20 for Cypripedium, Criosanthes, and Phragmipedium, this is probably the basal number for the subfamily. Although centric fission accounts for the upward aneuploid series in Paphiopedilum (2n = 26-44), higher metacentric arm ratios in the aneuploids than in the non-aneuploids suggest that centric fusion has occurred as well. It is argued that both fission and fusion have karyologically repatterned Paphiopedilum section Barbata with concurrent adaptation to florest floors. Under a vicariance model, the cladograms reveal geographic patterns in Paphiopedilum, Phragmipedium, and the SeZenipedium-Cypripedium clade with the primitive taxa southernmost. To explain the seemingly incongruous patterns with a necessary Laurasian origin, it is suggested that the southern­ most populations have followed habitats similar to the ancestral ones in re­ sponse to post-Miocene cooling. This mechanism may offer a partial explana­ tion for accumulation of primitive angiosperms on the Asiatic islands which have largely arisen since the Miocene. Contrary to popular belief, some slipper orchids are very advanced, and there is little evidence that the Cypripedioideae is a relic group at an evolu­ tionary dead end. CHAPTER I: INTRODUCTION The Cypripedioideae is a subfamily of the Orchidaceae known com­ monlyas the ladyslippers (various spellings) or slipper orchids. The subfamily is easily recognized by its unique flower (Fig. 1.1) which has a synsepal, a saccate labellum, a conspicuous staminode, and two fertile stamens. The slip­ per orchids are presumed to be most closely related to the subfamily Apostasi­ oideae, but the latter occasionally has three fertile stamens and lacks synse­ pals and saccate labella. * The Marie Selby Botanical Gardens, 811 S. Pa.hn Ave., Sarasota, FL 33577 129 130 SELBYANA [Vol 7 There are many popular and scientific accounts of slipper orchids; h w­ ever, no recent investigation has been made into relationships which m· ht elucidate evolutionary patterns within the Cypripedioideae. It is hoped t at the present work will help fill the void, and that it will provide a framew rk for understanding the subfamilial diversity. Most of the data have been 01- lected from nursery-grown plants, but a few wild populations have been ex­ amined so far as funds have permitted. Supplementary data have also been taken from literature sources, herbarium sheets, and occasionally from photo­ graphs. Because live material of Asiatic Cypripedium has been unavailable, . detailed taxonomic considerations within the plicate-leaved taxa are limited, ' but generic and infrageneric relationships are detailed among the condupli­ cate-leaved genera. THE GENERA There are two growth patterns in the slipper orchids (Fig. 1.2 and 1.3): (1) some species have thin, plicate leaves distributed on elongate stems (Cy­ pripedium and Selenipedium), and (2) some pave thick, coriaceous leaves forming basal, distichous rosettes (Phragmipedium and Paphiopedilum). There are several floral differences among :the genera. Selenipedium and Cypripedium have persistent perianths after anthesis, while the remaining gen­ era have deciduous perianths. Sepal vernatiop is perforate in the plicate­ leaved genera, valvate in Phragmipedium, and imbricate in Paphiopedilum. Selenipedium and Phragmipedium have axile placentation, and Cypripedium and Paphiopedilum have parietal placentation. Slipper orchids are found over much of the world but are notably absent from Africa and Australia. Cypripedium is temperate with a circum boreal distribution. In the Old World it ranges from England across Siberia, to southern China and southern Europe. In the New World it occurs over most of the North American continent south to Guatemala but is absent from ex­ treme southeastern United States. The genus is perhaps best developed in China with a second center of diversity in eastern North America. Selenipedi­ um is restricted to the isthmus of Panama and northern South America. Phragmipedium ranges from southern Mexico to tropical South America, but the greatest diversity is concentrated in Andean South America from Colom­ bia to Bolivia and Peru. Paphiopedilum has a complex range in the Old World tropics. It occurs from Hongkong west to Sikkim, south to Sumatra, east to New Guinea, and Bougainville. There exists a disjunct species in the Traven­ core Hills of southern India, but the greatest development of species is found on the southeast Asian islands, especially Borneo. Due to lack of revisionary work (especially with the Asiatic populations), the actual number of slipper orchid species is difficult to estimate. Both nar­ row and broad species concepts can often be applied to single populations with seemingly equal justification. In estimating species number it is best to give both conservative and liberal estimates based on available species descrip­ tions and names provided in Index Kewensis. Cypripedium may contain only 30 or as many as 50 species. The second estimate may be somewhat inflated by available names, but the opportunities for endemism and isolation in the mountains of China provide some justifica­ tion for this unusually high estimate. Only 6 species of Selenipedium have been described, and some may eventually be relegated to subspecific status. The species are not diverse in plant habit or in floral morphology relative to the other genera. Phragmipedium contains a minimum of 10 species, although 1984] ATWOOD: CYPRIPEDIOIDEAE 131 e fig. 1.2 Fig. 1.1 ·.\..---a b Fig. 1.3 Fig. 1.1 A generalized flower showing salient features: a. bract, b. synsepal, c. dorsal sepal, d. lateral petal with counter-clockwise spiral, e. lip or labellum, f. staminode. g. anther. Fig. 1.2 . A schematic representation of a plicate-leaved slipper orchid with spirally ar­ ranged leaves on an elongate stem: a. blade, b. sheath. Figure 1.3 A schematic representation of a conduplicate-Ieaved slipper orchid with leaves arranged in a distichous rosette. 132 SELBY ANA [Vol. 7 Garay (1979) has recognized 21. However, emphasis on singular characters (e.g., staminode shape) has undoubtedly led to taxonomic inflation. Paphio­ pedilum has a minimum of 60 species and a maximum of 80 species. Until extensive field work can be undertaken, firm bases for species recognition in Paphiopedilum will be sought in vain. There are 36 to 56 species among the plicate-leaved genera, and 70 to 101 conduplicate-Ieaved species. Altogether there exist between 106 and 157 slipper orchid species. HABITATS Slipper orchids are found in various habitats, although often absent from areas that would appear ideal. In eastern Vermont Cypripedium pubescens is found in calcareous bogs and experiences few effects ~om drought. Although the orchids may be locally common, their habitats in eastern Vermont are not. Bordering Lake Champlain in northern New York, the same species may be found on moist hillsides underlain with limestone bedrock. In this region the species may be found also in abandoned pastures with C. arietinum and C. reginae. Cypripedium pubescens in Michigan may be found not only in these habitats but also along roadsides as "weeds" where the roadbeds are constructed from crushed limestone. Occasionally C. pubescens may be found in full flower in lawns where it has become established in the lime­ stone substrate. Cypripedium acaule prefers acidic habitats with pines, oaks, and ericaceous shrubs, especially in areas which are semishaded. In Cape Anne, Massachusetts, I have observed that a June forest fire seemed to en­ courage the growth and development of C. acaule in following years. I have also observed C. acaule growing in the cracks of a highway within 4 years after paving. Cypripedium arietinum, although usually uncommon in New England, occurs abundantly along the northern shoreline of Lake Michigan in a lakeside zone disturbed by spring ice accumulation. Cypripedium candi­ dum prefers open prairies that are periodically burned. Little is known of the preferred habitats of Selenipedium. Dunsterville and Garay (1963) note that S. steyermarkii grows among "deep grass and head-high shrubs." Dunsterville and Dunsterville (1980) note that the same species may be found