THOMAS B. CROAT, 1994 33 Taxonomic Status of Neotropical Araceae Thomas B. Croat Missouri Botanical Garden P.O. Box 299 St. Louis, MO 63166-0299 USA INTRODUCTION of Araceae in South America is spotty, with some areas being relatively well known and The Araceae, with 106 genera and rough­ others, especially Andean areas of the con­ ly 3,200 species is nearly world wide in tinent, being very poorly known. Some ar­ distribution. There are two major centers eas for which floristic surveys have been of species diversity, in tropical Asia and conducted in the past thirty years or so are tropical America, with nearly an equal num­ relatively well known. This is especially true ber of indigenous genera, 43 for Asia and of Venezuela where extensive work has 36 for America (Croat, 1979). Of these to­ been done, especially by G. S. Bunting tals 33 are endemic to the American tropics (Bunting, 1975, 1979, 1986, 1988, 1989) but while 32 are endemic to Asia. Africa, a less also by Croat & Lambert (1986). The Ven­ important center of species diversity, has ezuelan flora contains 266 species with an only 19 indigenous genera with only 12 of additional 25 subspecies or varieties. them endemic. While the Paleotropics has The Guiana region is relatively well more genera than the Neotropics (60 versus known at least in part because it is relatively 36) the latter area contains roughly two­ species-poor rather than because of the ex­ thirds the species of the world's Araceae. tent of the collecting effort. Suriname was, Our level of knowledge of the systematics until recent years, the only part of the of the neotropical Araceae varies greatly Guianas that received much attention in from area to area, owing largely to recent regard to Araceae, this largely owing to the revisionary work or to the interest and area work of Jonker-Verhoef &Jonker (1953) in concentrated on by particular workers, e.g. Suriname. More recently, the whole region G. S. Bunting in Mexico (Bunting, 1965) is receiving more attention owing to work and Venezuela, Croat in Panama and Cen­ on the "Flora of the Guianas" project and tral America (Croat, 1978, 1983, 1986a, to the Araceae treatment being carried out 1986b, 1988a, 1991) and Croat & Grayum by Croat and collaborators. In addition, in Costa Rica. Central America is much more Bunting (in press) has completed the Ar­ well known than South America, largely aceae treatment for the Flora of the Vene­ owing to the more prolonged effort byaroid zuelan Guyana, the Venezuelan counter­ taxonomists in the region, but also owing part of this flora. to the fact that some parts of the area are Another example of a relatively well much less rich in species per unit area than known area is the state of Bahia in Brazil many parts of South America, especially the where Simon Mayo and other members of species-rich northwestern part of that con­ the Kew Garden staff, especially R. Harley, tinent (Croat, 1992). Most of the earlier work have made a number of expeditions. Mayo in Central America was undertaken by P. C. has also prepared a checklist for Brazil and Standley in a series of floristic works (Stan­ any reference to the number of species in dley, 1927, 1928, 1930, 1933, 1937, 1944). Brazil for any genus discussed in this paper Species diversity generally increases in relies heavily on his unpublished work. Central America as one approaches South Mayo has also worked closely with many America (Croat, 1986a, 1986b). Knowledge Brazilian botanists to encourage their par- 34 AROIDEANA, Vol. 17 ticipation in work with Araceae of Brazil fact that the species inhabiting the Amazon (see Aroideana for a discussion of these lowlands are in general wide-ranging, often efforts) . common species. Despite the presence of Parts of southern South America are by a few endemic species near the mouth of now also well known, where floristic treat­ the Amazon, e.g. Philodendron ecordatum ments for Argentina (Crisci, 1971) and Par­ Schott, the vast Amazonian region lying be­ aguay (Croat & Mount, 1988) have been tween the Atlantic coast and the foothills completed. In addition, a floristic treatment of the Andes has moderately few, mostly has been completed for the state of Santa Wide-ranging species. Species diversity in­ Catarina (Reitz, 1957). creases dramatically as one approaches the The published Flora of Peru (Macbride, foothills of the Andes in the west. Species 1936), though falling short of giving an ac­ occurring on the lowermost slopes of the curate picture ofthe species count for Peru, Andes tend to range widely in a north-south does come close to indicating the number direction, often from Colombia to Bolivia of species actually described for Peru, since, and thus tend not to be endemic. However, except for Anthurium sect. Pachyneurium some of the species of this region are cur­ (Croat, 1991), few groups have had many rently believed to be endemic. The degree species described from Peru since that pub­ of endemism increases as elevation increas­ lication. A more accurate accounting for the es on the slopes of the Andes and as the number of species of Araceae in Peru is terrain becomes more dissected with river published in the "Catalogue of the Flow­ valleys (Croat, 1994). ering Plants and Gymnosperms of Peru" To the east of the Amazon basin, es­ (Croat, 1993). Though not a thorough re­ pecially in the Guiana Highlands and in vision ofthe species occurring in Peru, this eastern Brazil, from the state of Bahia south list takes into account all species of plants almost to Uruguay, the rate of endemism is described for Peru as well as all species much higher. Nearly all the species occur­ represented only by identified herbarium ring in this region are endemic to eastern specimens which were able to be verified Brazil, and few range into the Amazon ba­ by experts for each family. The checklist sin. For example, five of the eight Anthur­ contains 210 species of Araceae for Peru ium species from Santa Catarina are en­ but it does not include any unpublished demic to eastern Brazil, including A. acu­ names and many species remain to be de­ tatum N. E. Br., A. gaudichaudianum scribed. Kunth, A. harrisii (Grah.) Endl., A. lacer­ While there is no completed Araceae dae Reitz, and A. pilonense Reitz. treatment for the flora for Ecuador, a re­ Though many species have been de­ cently published checklist for the Amazo­ scribed from eastern Brazil, by early aroid nian lowlands (Renner et al., 1990), which specialists, including Schott, K. Koch, and lists 92 species of Araceae (a few of them Engler, based on the early collecting efforts undescribed), gives some indication of the by botanists such as Glaziou, Regel, Riedl, species diversity of that part of Ecuador. and others, these areas remain poorly Unfortunately the Amazonian lowlands known, principally because of the taxo­ represent one of the most species-poor por­ nomic complexity in such groups as An­ tions of the country if its area is taken into thurium section Urospadix, which domi­ account, owing to the widespread nature nates the area. Perhaps the only group of of the species in that zone. aroids well known in the region are mem­ The above-mentioned treatments, though regional in nature, help to give an indica­ bers of the recently revised Philodendron tion of species diversity on the continent subgenus Meconostigma (Mayo, 1991). of South America, and any reference to spe­ The truly temperate parts of the conti­ cies counts for any genus is based on them. nent are devoid of aroids, and the subtrop­ The lowland Amazon basin is also rela­ ical portions of the continent, while con­ tively well known, principally owing to the taining a number of small, frequently en- THOMAS B. CROAT, 1994 35 demic genera in the tribe Spathicarpeae, Cauca Department, the department of An­ are also relatively species-poor. tioquia, and the department of Cundina­ Species diversity is high throughout the marca, especially around Bogota, were well extent of the South American Andes but collected in the late Nineteenth Century by especially along the northwestern slope ex­ collectors such as Lehmann, in time to have tending from Choco Province in Ecuador, their material included in the revisions of as well as on both the eastern and western both Schott (1860) and Engler (1905), many slopes in the Andes in the region of the areas have not been collected until recent equator and on the eastern slopes of the times. Andes in Peru. Species diversity is also rel­ Pichincha Province and a few other areas atively high in the Cordillera de Merida of of Pacific coastal Ecuador were well col­ western Venezuela, but remarkably less so lected by L. Sodiro (1901a, 1901b, 1903a, in the northern part of the Eastern Cordil­ 1903b, 1905a, 1905b, 1905c, 1906, 1907, lera of Colombia and on the entire western 1908) and 257 species (including 281 taxa) flank of the Eastern Cordillera in Colombia were described. Despite this, the region (Croat, 1992). Species diversity is also rel­ remains poorly known, largely because of atively low in the Central Cordillera of Co­ the inability to locate and study the widely lombia. In all cases high species diversity scattered and poorly documented collec­ is correlated with high precipitation and tions of Sodiro. Some Sodiro specimens are with the absence of prolonged dry seasons. deposited in European herbaria (Croat, Species richness is greatest between sea 1989), but most collections are depOsited level and middle elevations up to about in the poorly curated herbari um (Q PLS) of 1,500 meters.