The habitats and natural conditions of this species in Vietnam were described earlier (Averyanov et al., 2003, 2004). This species was fairly common in lowland and hilly areas of southern Vietnam, before wide land reclamation and deforestation.
Fig. 1, 2. Broad-leaved shady forests with bamboo on very steep granite and sandstone slopes of small mountain rivers are typical habitat of Paphiopedilum callosum var. callosum in Vietnam. (Photo 1, 2: Prof. Phan Ke Loc; digital correction: L.Averyanov)
Map 1. Distribution of Paphiopedilum callosum varieties in Vietnam. Localities of studied taxa are marked on the map of Vietnam with red and black (P. callosum var. callosum, black dots indicate localities of extinct populations), blue (P. callosum var. warnerianum) and yellow dots (P. callosum var. potentianum).
Regrettably, this species has become very rare, with nearly all its known populations seriously depleted by widespread commercial collecting. Growing at relatively low elevations, it is much more endangered than slipper orchid species occurring at higher elevations, where preservation of primary forests is usually better. Recent field explorations discovered a number of new populations of this rare species in remote regions of the country not previously explored. These investigations, as well as studies of numerous plants collected in Cambodia and Laos along the Vietnamese border, reveal remarkable variation of P. callosum, and make it possible to recognize at least three races in taxonomic rank of varieties. The key for their identification and a short illustrated survey of these intraspecific taxa in the flora of Vietnam are presented below.
Paphiopedilum callosum (Reichenb.f.) Stein, 1892, Orchideenbuch: 457 - Cypripedium callosum Reichenb.f., 1886, Gard. Chron., 2 Ser., 26: 326.
Type: Thailand, Regnier s.n. (Holotype – W).
Key for Identification of P. callosum Varieties found in Vietnam
1. Petals strongly sigmoid, distinctly down deflexed, usually more than 5 cm long,
commonly with ciliate warts along upper and lower margin; median sepal usually
more than 5 cm wide ............. 1. P. callosum var. callosum
Petals hardly sigmoid or straight, borne at an angle of 45° to the horizontal, usually less than 5 cm long, with few ciliate warts along upper margin or without marginal warts at all; median sepal usually less than 5 cm wide ........................ 2.
2. Petals bear few warts only on the upper margin ............................. 2. P. callosum var. warnerianum
Petals lack the marginal warts ....................... 3. P. callosum var. potentianum
1. P. callosum var. callosum.
P. callosum var. angustipetalum Guillaumin, 1924, Bull. Soc. Bot. France, 4 Ser., 24: 551.
Fig. 3-5. Intact populations of Paphiopedilum callosum var. callosum commonly consist of hundreds of large clumps of flowering size (fig. 3-5). Usually plants grow as terrestrial rosulate herbs, which flower in nature in May-June (fig. 4) and develop fruits (fig. 5) in November-December. (Photo 4: Prof. Phan Ke Loc; digital correction: L.Averyanov)
Type: Cambodia, Geoffrey, 338 (Holotype – P). P. amabile auct. non Hallier f.: Guillaumin, 1937, Bull. Mus. Paris, 2 Ser., 9: 217; id., 1961, ibid., 2 Ser., 33, 3: 333; Gagnep., 1950, Bull. Mus. Hist. Nat. Paris, 2 Ser., 22, 5: 628; Seidenf., 1975, Contrib. Revis. Orch. Fl. Cambod. Laos Vietnam: 88; Aver., 1988, Prelim. List Vietnam. Orch. 2: 31; Pham Hoang Ho, 2000, Ill. Fl. Viet. 3: 762.
This is the most widespread and common race in Eastern Indochina, including southern Vietnam (map 1). Closed forests on steep rocky stream slopes are the most common habitat of this variety. Different kinds of tall bamboo are a common component of shrubby stratum in such forests, particularly on very steep slopes and rocky bluffs (fig. 1, 2). Granite and sandstone are the usual parental rocks in habitats of P. callosum var. callosum in studied areas. In intact populations plants often form a continuous cover with many hundreds of large clumps. Usually they grow as terrestrial clumps of clustering herbs on rich soils covered with more or less thick leaf litter (fig. 3-5); a few individuals were occasionally observed growing as lithophytes on shady mossy boulders. In their natural habitats plants flower in May-June (fig. 4) and develop fruits in November- December (fig. 5). Observed variation of coloration, shape and size of flowers in populations of P. callosum var. callosum is very wide. Plants in most studied colonies have large flowers with strongly deflexed, more or less heavily spotted, petals that are distinctly warty along upper and lower margins (fig. 6-8). Flowers of other plants petals bear few spots and barely pronounced warts on the lower margin (fig. 9, 10). Sometimes such plants with this feature closely approach P. callosum var. warnerianum. Some plants in natural populations of P. callosum var. callosum exhibit a tendency towards albinistic forms. Occasionally such plants lack only a part of purple pigments (fig. 11), but in some rare forms anthocyanins are completely absent (fig. 12). Similar forms are known in cultivation under the names var. sanderae (Hort.) Braem and var. viridiflorum (Hort.) Pfitzer. (Averyanov et al., 2003).
Fig. 6-8. Typical flowers of Paphiopedilum callosum var. callosum with strongly deflexed, more or less heavily spotted, petals, warty along upper and lower margins. © L. Averyanov
Fig. 9, 10. Flowers of some plants in populations of Paphiopedilum callosum var. callosum bear no spots and few hardly visible warts on the lower margin of petals. Due to these features, such plants approach to P. callosum var. warnerianum. © L. Averyanov
Fig. 11, 12. Sub-albinistic (fig. 11) and albinistic forms (fig. 12) were occasionally observed in populations of Paphiopedilum callosum var. callosum in Vietnam. When sub-albinistic forms are sometimes more or less common, completely albinistic forms occur very rarely (Lam Dong province, southern Vietnam). Similar forms are known in cultivation under the names var. sanderae (Hort.) Braem and var. viridiflorum (Hort.) Pfitzer. (Photo 12: Mr. Son Ha; digital correction: L.Averyanov)
2. P. callosum var. warnerianum (T. Moore) P.J. Cribb ex Aver., comb. nov.
— Cypripedium barbatum var. warnerianum T. Moore, 1878, Warner Select. Orchid., 3 Ser., Pl. 3, t. 11.
Fig. 13-15. Typical flowers of Paphiopedilum callosum var. warnerianum are distinctly smaller than flowers of type variety. Their petals are regularly broad and spread, without warts along the lower margin. Coloration of flowers varies from light pink/green to deep purple. © L. Averyanov
Lectotype: T. Moore, 1878, l.c. Pl. 3, t. 11 (Cribb, 1998, p. 337). Cypripedium callosum var. sublaeve Reichenb.f., 1888, Gard. Chron., 3 Ser., 3: 331. -Paphiopedilum callosum subsp. sublaeve (Reichenb.f.) Fowlie, 1972, Orchid Dig. 36: 145. - P. sublaeve (Reichenb.f.) Fowlie, 1979, Orchid Dig. 43: 22. - P. callosum var. sublaeve (Reichenb.f.) P.J.Cribb, 1987, Gen. Paphiopedilum: 188.
Type: Thailand, cult. Measures s.n. (Holotype – W). Paphiopedilum thailandense Fowlie, 1979, Orchid. Dig. 43:220, nom. nud.
Fig. 16. Occasionally flowers of Paphiopedilum callosum var. warnerianum have more or less heavily spotted petals that are not too usual for this variety. © L. Averyanov
Fig. 17. Rare form of Paphiopedilum callosum var. warnerianum with two-flowered inflorescence. © L. Averyanov
Fig. 18. Sub-albinistic form of Paphiopedilum callosum var. warnerianum with insufficiency of purple pigments. © L. Averyanov
Fig. 19. Sub-albinistic form of Paphiopedilum callosum var. potentianum discovered in lowlands near Cambodian border. © L. Averyanov
Peninsular Thailand and adjacent northwest Malaya are reported as the main distribution area for this variety (Cribb, 1998), which is sometimes regarded as an “intermediate” hybrid form between two vicarious species—P. callosum (distributed in mainland Southeast Asia) and P. barbatum (from Malacca Peninsular and northern Sumatra). In this connection, its finding in southern Vietnam is rather surprising. In Vietnam, P. callosum var. warnerianum was found in warm lowland forests near the Cambodian border (map 1). Here this plant is very rare, but some collections from Cambodia provide certain evidence that this variety may be not uncommon in lowland areas of southeast Indochina including eastern Cambodia and southern Laos. The discovery of P. callosum var. warnerianum in this area suggests that either this variety evolved independently or it may indicate close genetic relations between floras of southeastern Indochina and the Malacca Peninsula, also exhibited by some other plant genera and species (Averyanov et al., 2003). Studied plants originating from Vietnam and allied regions of Cambodia typically have small flowers with broad spreading petals bearing only a few warts along their upper margin and no warts on their lower side (fig. 13-15). Usually petals are uniform green to pinkpurple with darker longitudinal veins. However, some samples have spotted petals with more or less numerous large dark maroon-brown spots (fig. 16). Occasionally such plants bear two flowers on a single floral stalk (fig. 17). Tendencies for formation of subalbinistic and albinistic forms can be seen in populations of P. callosum var. warnerianum (fig. 18), similar to the type variety. All observed specimens flowered in the studied area in May-June.
3. P. callosum var. potentianum (O.Gruss et J.Roeth) P.J. Cribb, 1998, Gen.
Paphiopedilum, ed. 2: 337. – P. potentianum O. Gruss et J. Roeth, 1995, Caesiana 5: 39.
Type: Thailand, cult. E. et G. Potent, Roth s.n. (Holotype – HAL).
This variety was described based on plants imported from Thailand without indication of their exact origin. This gives no guarantee that the plants were really collected on the territory of Thailand, which imports many plants from neighboring countries. In Vietnam very similar plants were found in lowland warm-growing forests of Cambodian type near the Cambodian border (map 1). Such a finding may indirectly indicate lowland areas of Cambodia and southern Laos as a possible area of distribution of this very rare taxon. Like both previous varieties, plants of P. callosum var. potentianum also demonstrate certain trends towards formation of sub-albinistic forms with a deficit of purple pigments. Some of these produce flowers of particular elegance (fig. 19).
On the basis of our observations, it looks as if these varieties merge into one another with more or less numerous intermediate forms. The understanding of their nature obviously needs more field studies of wild intact populations. Such study is urgently needed because survival of these varieties in nature is uncertain and the prospect for the continued existence of this lowland species, in the wild, is very bleak due to the rapid transformation of lowland areas for agriculture and economic development zones. The best hope is that some of these plants will be collected for cultivation before all become extinct.
Field and laboratory studies, results of which are presented in this paper, were made under the auspices of these exploration programs: "Population studies of endemic Paphiopedilum species in northern Vietnam" American Orchid Society, 2001-2002; "Discovery of endemic orchid flora in remote limestone areas of Northern Vietnam" American Orchid Society, 2004; “Exploration of rocky limestone flora and vegetation in Bac Kan province, northern Vietnam” U.S.A. National Geographic Society, 2004, # 7577-04; and investigation program of Vietnamese Botanical Conservation Program supported from Henry Luce Foundation (U.S.A.).
Averyanov L., Cribb, P., Loc, P. K., and N. T. Hiep. 2003. Slipper Orchids of Vietnam. With an Introduction to the Flora of Vietnam. Royal Botanic Gardens, Kew. Compass Press Limited.
Averyanov, L.V., Loc, P. K., Hiep, N. T., and D. K. Harder. 2003. Phytogeographic review of Vietnam and adjacent areas of Eastern Indochina. Komarovia. 3:1-83.
Averyanov L., Cribb, P, Loc, P. K., and N. T. Hiep. 2004. Lan Hai Viet Nam. Giao Thong van tai Publishing house. Ho Chi Minh City (Vietnamese ed., 2003). Cribb P. 1998. The Genus Paphiopedilum. Natural History Publications (Borneo) & Royal Botanic Gardens, Kew.
Leonid V. Averyanov
Herbarium, Komarov Botanical Institute of the Russian Academy of Sciences