Small to large terrestrial, lithophytic or epiphytic herbs; roots elongate, fibrous; rhizome short to elongate. Shoots short, erect, leafy, clustered or less frequently well spaced, glabrous, the base enclosed by two to four sheathing sterile bracts, three- to several-leaved above. Leaves one to several, coriaceous, conduplicate, spreading or suberect, ligulate, elliptic, or oblong, obtuse to acute, often tridenticulate at apex, green, bluish green, or chequered or tessellated with dark and lighter green on upper surface, lighter green below, sometimes finely spotted or flushed with purple at base or all over, glabrous, ciliate or not on the margins. Inflorescence terminal, one- to many-flowered; rachis terete, hairy, glandular or glabrous; bracts conduplicate, elliptic, lanceolate, ovate or oblong, green, sometimes spotted or flushed or striped with purple, ciliate or not. Flowers usually showy, concolorous or bicoloured; pedicel obscure to short; ovary unilocular, three-ribbed, glabrous or hairy. Dorsal sepal erect to hooded over lip, ovate, lanceolate, obovate or elliptic, obtuse, acute or acuminate, glabrous or pubescent on the outer surface, sometimes pubescent within at base, ciliate or not. Lateral sepals usually fused to form a concave synsepal that is more or less similar to the dorsal sepal, sometimes keeled on outer surface. Petals free, spreading or pendent, flat, reflexed or spiralling, elliptic, ovate, lanceolate, linear-lanceolate, linear or oblanceolate, rounded, obtuse, acute or acuminate at apex, often pubescent in basal half within, usually ciliate. Lip deeply pouched and inflated, slipper-shaped or urn-shaped, with more or less pronounced incurved side lobes, hairy within especially on lower surface, glabrous or hairy on outer surface; front margin incurved or not. Column short, stalked, porrect; anthers two, bilocular, borne on short obtuse to acute filaments; pollen powdery or viscid; staminode terminal on column, sessile or shortly stalked, transversely reniform, oblong, ovate, obcordate or linear, flat, convex or longitudinally conduplicate, glabrous to papillose or finely pubescent, ciliate or not; stigma stalked, dependent, tripartite, more or less papillose. Capsule erect to pendent, three-ribbed, cylindrical to almost ellipsoidal. (PC).
The range of Paphiopedilum extends from India eastward across southern China to the Philippines and throughout south-east Asia and the Malay Archipelago to New Guinea and the Solomon Islands. Of the seven Indian species, six are confined to the north-east, along the foothills of the Himalaya from eastern Nepal to the Naga Hills, and also in the Khasia Hills. One species, P. druryi, is found only in southern India, in Kerala State, over 2000 km from the nearest Paphiopedilum locality to the north.
Five species of Paphiopedilum have been reported as growing epiphytically. Paphiopedilum parishii, P. lowii, and P. villosum are usually found growing on trees, whereas P. hirsutissimum and P. glanduliferum are facultative epiphytes. The remaining species are either terrestrial or lithophytic.
Most of the species are to be found growing in small colonies with their roots in leaf litter, often spreading some distance from the base of the plant. In some species of subgenus Brachypetalum (P. concolor, P. bellatulum, P. niveum) and in subgenus Paphiopedilum sects. Corypedilum (P. stonei, P. sanderianum, P. philippinense), Pardalopetalum (P. dianthum) and Paphiopedilum (P. hirsutissimum var. esquirolei, P. barbigerum), for example, the plants will grow with their roots attached to a rocky substrate and are true lithophytes.
Species of Paphiopedilum are found from India east across south-east Asia to the Philippines in the west and from southern China in the north, south to the Malay Archipelago, New Guinea and the Solomon Islands. Several species are found at sea level, for example P. philippinense and P. glanduliferum, but the majority are found in hill country, sub-montane and montane conditions. In the Himalayas, P. fairrieanum grows at elevations up to 2200 m, and P. villosum up to 2000 m; likewise in western Yunnan in China, both P. tiginum and P. armeniacum have also been reported from 2000 m. In Borneo P. hookerae var. volonteanum has been found at 2300 m elevation on the slopes of Mt Kinabalu.
The genus is found over an elevational range from, sea-level to about 2300 m, but only in P. hookerae, P. bullenianum, and P. lowii has a species been found over a wide elevational range, the first of these with the most extensive range. Paphiopedilum hookerae var. volonteanum, in Sabah, grows on ridges in lower montane forest at 900 m and again on Mt Kinabalu on a landslide at c. 2300 m elevation. On Mt Kinabalu P. lowii, usually a lowland species, has been recorded from c. 1600m.
The majority of Paphiopedilum species grow in lower montane evergreen or seasonally deciduous forest, often on the forest floor in shade. A few species such as P. exul and P. philippinense have been recorded as growing in exposed sunny places. More commonly, though, species such as P. niveum, P. philippinense and P. rothschildianum, which will grow in more open positions, are seldom exposed to direct sunlight for any length of time during the day. On Mt Kinabalu in Sabah, P. rothschildianum grows where dappled sunlight hits the plants only in the afternoon. In contrast some of the tessellated-leaved species grow in deep shade. In Java and Borneo, P. javanicum and its var. virens grow on the forest floor in places where no direct sunlight penetrates.
In many areas where Paphiopedilums grow, the rainfall and consequent humidity are high, but rainfall is usually seasonal, and plants in such areas often have to survive considerable dry periods. The thick coriaceous leaves are ideally adapted to survive periodic droughts, and plants recover rapidly when the rains return. Most growers who have received plants through the post will support the view that Paphiopedilums can survive well in such adverse conditions. (PC).
Paphiopedilums are one of the most popular groups of orchids in cultivation. They are grown as either pot plants or for their cut flowers, both trades being substantial. They are prized for their long-lasting, substantial, and unusual flowers. Leaf shape and colour are variable: species and hybrids of subgenera Parvisepalum and Brachypetalum and of section Barbata have tessellated leaves, sometimes marked with purple beneath; the rest have green leaves that are paler below. Plants with single flowers or with several-flowered inflorescences are available among both the species and hybrids. Flowers range in size greatly, the smaller species having flowers of 5 cm or less across, whereas some hybrids have enormous, almost circular flowers up to 15 cm in diameter or more. The extraordinary and highly sought-after P. rothschildianum has a petal spread of up to 32 cm. The range of flower colour is immense, from white through yellows, greens, browns, purples to reds, or combinations of any of these. Some of the species and complex hybrids have spotted sepals and/or petals and glossy floral segments. (PC).
Van der Piji and Dodson (1966) suggested that Paphiopedilum and Phragmipedium have trap flowers that are, at least in part, fly-pollinated, whereas Cypripedium and possibly Selenipedium flowers are bee-pollinated. More recently Bänziger (1996) provided a detailed survey of theories and studies of slipper orchid pollination discussed below. Van der Piji and Dodson (1966) and Atwood (1985) cited the lurid floral coloration and the 'curious furry warts' and spots on the floral segments of some species as typical of adaptations in flowers that attract flies. The long tail-like petals of P. sanderianum, for example, might serve the same function. Cross-pollination by insects is certainly prevalent in Paphiopedilum. Self-pollination such as that seen in Phragmipedium lindenii in which the lip is petaloid is absent in the genus. Delpino (1873) mentioned an ‘odore spermatico-urinoso' in P. villosum and P. purpuratum and suggested basic myophily for the group, corroborated by his discovery of bluebottle flies trapped in the lip of P. barbatum in a greenhouse in Italy. Schlechter (1927) made similar observations, and Ziegenspeck (1928) found the same in P. insigne. Atwood (1985) has observed syrphid flies in the lip of P. hennisianum in cultivation in Florida. The only detailed studies in the field of pollination are of P. rothschildianum and other Bornean species on Mount Kinabalu by Atwood (1985) and of P. villosum in north Thailand by Bänziger (1996). The syrphid fly, Dideopsis aegrota, was found to be the pollinator of P. rothschildianum. The flowers, emitting a 'peppery or spicy fragrance', are considered to mimic brood sites to attract gravid female flies to the staminode where they lay their eggs. Atwood found as many as 76 eggs on a single staminode. After alighting on the staminode, which has a glabrous front, the fly falls into the lip and can only escape by crawling up the hairs, which lead it beneath the stigma and anthers in turn, and emerging eventually from one of two exits on either side of the base of the column. Pollination is effected when the fly repeats the manoeuvre in a second flower. The fly apparently gains no benefit from its experience as the eggs either do not hatch or else the larvae die on hatching from lack of food. Likewise, the fly receives no food benefit from its visit because the flower lacks nectar. Atwood suggested that the glandular hairs on the staminode mimic a colony of aphids, the normal brood site of the fly. Atwood (1985) also studied colonies of P. hookerae var. volonteanum and P. javanicum var. virens which grow on Mount Kinabalu as well but was unable to determine the pollinators. From eighteen observed flowers of the latter he noted that three had been pollinated in a six-week period after anthesis. The high seed-production in successful pollinations no doubt makes up for this low success rate. A single syrphid egg was found on the staminode of P. hookerae var. volonteanum, but as it was growing near P. rothschildianum little could be concluded from the observation. Cribb (1998b) reported collecting a dead syrphid fly trapped between the base of the lip and column of P. javanicum var. virens on Kinabalu. The fact that it had been trapped and died suggests that a smaller species might be the normal pollinator. He also found syrphid eggs on the staminode of P. philippinense in cultivation in Vanuatu in the south-west Pacific. Atwood's (1985) study gave no clue as to the function of the long petals of P. rothschildianum, and his work suggested that the floral fragrance emanates from the centre of the flower rather than from the glandular petal tips as noted in Phragmipedium by Vogel (1962). Bänziger (1996) also provided strong circumstantial evidence that syrphid flies pollinate P. villosum. He studied several colonies of this epiphytic species in the evergreen hill forests of north Thailand. Paphiopedilum villosum flowers over a period of four and a half months, and individual flowers can last several weeks before dying. Pollen capture was observed in 15 cases, mainly involving female hover-flies of Episyrphus alternans, Syrphus falvifacies, and Betasyrphys serarius. He surmised that the hover-flies are lured mainly by food deception. Long-distance attraction is probably by the urine-like scent of the flowers; close-range attraction is by the glittering staminode which may mimic droplets of honeydew or moisture. The wart in the centre of the flowers appears to provide an attractive potential perch for the hover-flies. However, it is slippery and they fall into the slipper-shaped lip, the incurved margins of which prevent wing action so that the insect cannot fly out of the lip's orifice. Escape is along a ladder of hairs up to the stigma and anthers in turn and then out by the base of the column. The pollen, which is very sticky and remains viable on the flower for about eight weeks, adheres to the back of the hover-fly. If the hover-fly visits another flower and is trapped, the pollen can be transferred to the stigma of that flower as the insect squeezes beneath the stigma, the flexibility of the lip pressing the insect against the papillose stigma surface. The flowers of P. delenatii, P. micranthum, P. armeniacum, and their allies strongly resemble those of some species of Cypripedium and Phragmipedium. These species of Paphiopedilum may be bee-rather than fly-pollinated. In P. micranthum, for example, the staminode resembles that of Cypripedium henryi not only in shape and attitude but also in coloration. The latter is a close relative of C. calceolus, which has been the subject of several studies (e.g. Nilsson 1979) of bee pollination. (PC).