DSpace at VNU: The genus Cycas (Cycadaceae) in Vietnam

The Botanical Review 70(2): 134-193 The Genus Cycas(Cyeadaceae) in Vietnam KEN D HILL National Herbarium of New South Wales Royal Botanic Gardens Sydney 2000, Australia HI~P T NGUYEN Institute of Ecology and Biological Resources Nghia Do, Cau Giay, HanoL Vietnam AND Prt~q K Loc Department of Botany University of Science, VNU Thanh Xuan, HanoL Vietnam I II III IV V VI VII VIII IX X XI Abstract Introduction Generic Concepts Species Concepts Hybridism Conservation Taxonomic Treatment Species Known from China That May Be Expected to Occur in Vietnam Doubtful and Excluded Names Acknowledgments Literature Cited 134 135 135 136 136 137 137 188 190 191 191 I A b s t r a c t The genus Cycas is revised for Vietnam Twenty-four species are enumerated, nine o f them described as n e w (C aculeata, C brachycantha, C collina, C condaoensis, C pachypoda, C dolichophylla, C fugax, C hoabinhensis, and C tropophylla) Descriptions o f two Chinese species k n o w n to occur close to the China-Vietnam border are also provided A n e w combination is made for C bifida (formerly C rumphii vat bifida) The species are placed within an infrageneric classification previously outlined Distribution o f all taxa is mapped, and a key to species is provided Illustrations are provided for n e w and poorly k n o w n taxa where adequate Copies o f this issue [70(2)] may be purchased from the N Y B G Press, The New York Botanical Garden, Bronx, N Y 10458-5126, U.S.A.; nybgpress@nybg.org Please inquire as to prices Issued 03 September 2004 2004 The New YorkBotanicalGarden 134 CYCAS 1N VIETNAM 135 material has been available Previous reports of C circinalis and C rumphii from Vietnam are discussed Lectotypes are designated for C balansae, C chevalieri, and C elongata, and a neotype is designated for C pectinata II Introduction The genus Cycas was first recorded from Vietnam by de Loureiro (1793), with his description of the new species Cycas inermis, based on collections he had made in Cochin China (southern Vietnam) in 1787 Although the third species of Cycas to be described, C inermis has at no stage been properly understood Since that date, eight additional taxa have been described as new in the catalog of the flora of Vietnam The first of these were C tonkinensis and C bellefontii, described by Linden and Rodigas (1885, 1886) Both were described from living plants in cultivation that had been collected in Tonkin (northern Vietnam), and no herbarium material was preserved (see doubtful and excluded names below) Warburg described C balansae from near Hanoi in 1900, and Thiselton-Dyer described C micholitzii from Annam (central Vietnam-Laos) in 1905 Finally, Leandri described C chevalieri from northern Vietnam and C pectinata var elongata from southern Vietnam in 1931 Taxa previously known from other areas that have also been recorded from Vietnam are C pectinata Buch.-Ham and C siamensis Miq The names C circinalis L and C rumphii Miq have at different times been wrongly applied to Vietnamese taxa Other names misapplied to plants from Vietnam have been C undulata and C miquelii (see excluded names, below) The comprehensive account of the genus by de Candolle (1868), recorded only Cycas inermis from the region of Vietnam, largely on the basis of the notes published by de Loureiro De Candolle had also followed Miquel (1851) in misapplying the name C inermis to specimens of C revoluta (see below) Pilger (1926) recorded only C siamensis and C micholitzii from Vietnam Schuster (1932) included C tonkinensis in C circinalis var undulata, but also ineluded material of the C rumphii complex from the Marianas, together with material from Vietnam, in a confused concept Schuster also recognized C siamensis and C michoBtzii from Vietnam, but then held C inermis and the quite unrelated C balansae as subspecies of C siamensis Leandri (1931) had added C immersa to the Vietnam catalog, and subsequently Schuster correctly placed C immersa in the synonymy of C siamensis (in subsp, siamensis sensu Schuster), although he included a number of unrelated species in the other subspecies he erected within C siamensis The regional account by Leandri (1931) listed 10 species occurring in Vietnam but misapplied the names Cycas circinalis, C rumphii, and C immersa Ho and Duong (1960) recorded only species but again misapplied the three names above Ho later (1991) added an eighth species, C inermis, again misapplying the above names and the latter name as well Hi~p and Vidal (1996) recorded species, correctly placing C immersa in the synonymy of C siamensis but otherwise followed the same misapplications (discussed below under relevant species) More recent studies have gradually shown that the cycad flora of Vietnam is substantially richer in fact, probably the richest of the region (Hi~p & Loc, 1997, 1999) IlL Generic Concepts The recently described genus Epicycas (de Laubenfels & Adema, 1998) is herein placed in the synonymy of Cycas When characters that are inconsistent are excluded, the new genus is defined solely on the possession of a bulbous underground base However, even this character is neither wholly consistent within species nor restricted to the species placed in the new genus Moreover, of the species placed within the new genus, a number have what are clearly sister 136 THE BOTANICAL REVIEW species that were left in the genus Cycas; for example Cycas siamensis and C elongata (both placed in Epicycas) are closely allied to C pectinata, and C taiwaniana is close to the group placed in Epicycas tonkinensis (see excluded species below) Grouping characters (or synapomorphies) supporting these relationships are discussed below under the relevant sections IV Species Concepts The genus Cycas shows a complex geographical replacement pattern throughout its range, often with many closely related entities Although these taxa are often similar in many respects, the homoplasy evident in the defining characters does not always allow unequivocal aggregation into groups that could be treated as species with subordinate subspecies In order to satisfactorily separate and recognize groups of populations that show real, albeit sometimes small, differences, these groups are treated herein as distinct species This rather narrow view of species is considered preferable to the arbitrary submerging of these recognizably distinct and true-breeding groups of populations into broader and less meaningful "species" and the consequent loss of information on the real diversity of these plants Species definition is complicated by the variability of some of the characters that have been traditionally used to separate taxa Development of spines on petioles is often variable within populations and often changes with age in most taxa Microsporophylls vary considerably in size and shape from base to apex of the cone; in particular, the apical spine is reduced or absent on the lowermost sporophylls, gradually increasing in size toward the apex or toward the center of the cone (see also Amoroso, 1986) Megasporophylls also vary, often widely, in size, shape of lamina, and number of ovules This can depend on their position within a growth flush, the first and last produced often being markedly smaller and less elaborate than those in the center Because many herbarium collections are fragmentary, incomplete, and often sterile, many characters are often not present or recorded Comprehensive field study is thus essential to the understanding of the ranges of variation and of characters that distinguish taxa All species discussed herein have been examined in the field V Hybridism The problem of hybridism in Cycas was introduced elsewhere (Hill, 1992, 1996) The lack of pollinator specificity, when combined with the apparently weak inherent fertility barriers, results in the major reproductive barrier between Cycas species in nature being geographical separation Natural populations of Cycas species are usually widely separated geographically, and some breakdown of reproductive isolation would therefore be expected where different species have spread to within pollination range of each other A number of natural occurrences are postulated to be of just such hybrid origin These are morphologically intermediate between the putative parent species and, in the cases of postulated hybrid swarms, show the high degree of variability to be expected from Mendelian segregation in the second and later generations Hybrids and hybrid or intergrading populations have been recorded from throughout the range of Cycas, wherever different species grow in relatively close proximity Examples from Vietnam include intergradation between C dolichophylla and C.ferruginea east of Thai Nguyen, between C collina and C dolichophylla west of Moc Chau, and between C dolichophylla and C bifida west of Thai Nguyen (all are cited below under the first species of the pair listed) CYCAS IN VIETNAM 137 VI Conservation Populations of many Asian species appear to have declined, sometimes dramatically, over the past century However, there is no comparative data to support this impression, and evidence for the decline is largely anecdotal and circumstantial Several causative factors for this decline can be observed in action today, however, even though quantitative data on the effects are not available Two principal threats to cycads exist in Vietnam at present, habitat loss and selective removal of plants from the wild for trade or utilization Some but not all species occur in reserved areas already proclaimed, but enforcement within these areas is sometimes difficult There is, however, a growing interest in habitat and species conservation within Vietnam, and additional reserved areas are being evaluated and declared Only one Vietnamese species, Cycas micholitziL was listed in the now out-of-date (for this region) IUCN 1997 Red List of Threatened Plants (Waiters & Gillet, 1998) Species treated below are allocated provisional conservation status codes under the new coding system devised by the IUCN (IUCN, 1994) Conservation status of all species is summarized in Table I VII Taxonomic Treatment CYCASL., Sp PI.: 1188 1753 LECTOaWPE:Cyeas circinalis L.; designated by Stevenson in Jarvis et al (1993) Dioecious palm-like shrubs with aerial or subterranean, pachycaulous, cylindrical stems clad with persistent leaf-bases Leaves loosely pubescent when young, pinnate, spirally arranged, produced in seasonal growth flushes interspersed with cataphylls, lower pinnae often reduced to spines Longitudinalptyxis erect or rarely reflexed, horizontal ptyxis circinate Pinnae with a single thick midrib and no lateral veins; stomata confined to abaxial surface in most species; individual ptyxis involute Trichomes transparent, branched or simple Mierosporophylls aggregated into determinate cones and bearing numerous microsporangia (pollen sacs) on abaxial surfaces, with a simple sterile apex, which is often produced into an upturned spine; microsporangia opening by slits; pollen cymbiform, monosulcate Megasporophylls spirally arranged in an indeterminate terminal rosette with the central axis continuing vegetative growth Ovules two to many (rarely one), marginally inserted on the stipe and directed obliquely outward ("ascending"); sporophyll apically dilated into a pinnatifid, pectinate, toothed, or entire lamina Seeds with a yellow, orange, or brown fleshy outer sarcotesta and with or without spongy tissue beneath the inner woody sclerotesta Endosperm haploid, derived from the female gametophyte Embryo straight, with cotyledons that are usually united at the tips and a very long, spirally twisted suspensor; seeds platyspermic; germination cryptocotylar About 90 species, chiefly Australian (27 species) and Indo-Chinese (about 35 species) The genus also occurs in the Malesian region, Japan, and India, extending to Micronesia and Polynesia, Madagascar, and East Africa Plants are commonly understory shrubs in forest, woodland, or savanna habitats Four sections have been recognized (Hill, 1995), although there has been disagreement on subgeneric division (Wang, 1996; de Laubenfels & Adema, 1998), and, in the light of improved understanding of the genus, none of the proposed systems would appear entirely adequate (Hill, 2004) Three clear groups, regarded below sections, occur naturally in Vietnam (Fig 1), and a fourth is represented by one widely cultivated species Vietnam has the greatest diversity at the sectional level and the highest number of species of any country except Australia 138 THE BOTANICAL REVIEW Table I C o n s e r v a t i o n status o f V i e t n a m e s e c y c a d s Reserved Cycas species C aculeata C balansae C brachycantha C chevalieri C clivicola C collina C condaoensis C dolichophylla C elongata C ferruginea C fugax C hoabinhensis C inermis C lindstromii C litoralis C micholitzii C multipinnata C sexseminifera C bifida C pachypoda C pectinata C siamensis C simplicipinna C tanquingii C tropophylla Occurrence outside Vietnam China ?Laos Cambodia, Malaysia, Thailand ?Laos China 1997 Red List IUCN 1994 status Population size Present decline Range y y y VU/CR? LRnt LRnt LRnt LRnt ?250-2500 >10,000 >10,000 >10,000 >10,000 ?low low low low low 20 400 50 100 1000 ?20-50 20-50 VU A2c VU D2 VU A2c VU A2c LRnt DD/CR? EN A2c DD/LR? VU A2c LRcd 2500-10,000 2500-10,000 >10,000 >10,000 >10,000 ?250-2500 2500-10,000 >10,000 >10,000 >10,000 low stable low high low high high high high low 200 20 500 100 50 200 50 200 200 1000 20-50 10,000 1000-2500 > 10,000 > 10,000 2500-10,000 >10,000 high low low high low low 200 ?300 500 100 20 20-50 20-50 y VU A2c DD/CR LRnt VU A2e DD/LR? VU A2c y VU A2c >10,000 low 1000 20-50 y LRnt >10,000 low 1000 20-50 N y NT LRnt >100,000 >10,000 stable low 100 50