Neotropical Moss Floras: Species Common to North and South America

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Hochschulschriftenserver - Universität Frankfurt am Main 1 Tropical Bryology 10: 1-6, 1995 Neotropical moss floras: Species common to North and South America. Claudio Delgadillo M. Departamento de Botánica, Instituto de Biología, UNAM, Apartado Postal 70-233, 04510 México, D.F. Mexico. Abstract. North and South America share about 675 species that show two basic patterns, namely, those with a continuous range and those with a disjunct distribution. Both may have resulted from step-by- step migration, but the latter, including 118 species, may be due to break up of previous distributions by post-Tertiary tectonic and climatic changes or by long-distance dispersal. The distribution of vascular plants inclu- shared families of flowering plants could be des many genera common to North and South referred to Gondwanan or Laurasian origins America (Johnston 1940, Miranda 1959). Some (Raven & Axelrod 1974). Gentry (1982), in of them have widespread ranges while others discussing the floristic richness of the neotropics, exhibit disjunct distributions between both land pointed out that with the closure of the Central masses (Good 1964, Rzedowski 1978). While American isthmus many South American taxa long-range dispersal has been proposed as an moved north to completely dominate the Central explanation (Raven 1963), it is often assumed American lowlands and that most of this invasion that the shared taxa resulted from past plant is so recent that there has been little differentiation migrations even though certain such patterns as at the species level. In the upper elevations of the bicentric distributions are difficult to explain Costa Rica the vascular flora shows distinct links because the herbaceous and woody species seem with northern Central America and Mexico, and to represent different periods of floristic inter- with the Andes; at the generic level, 95% of the change (Johnston 1940). flora is shared with the Andean region (Cleef & Chaverri 1992). This seems to reflect dispersal Modern studies have proposed origins, trends that occurred in the area. Hammen and times and routes of migration for vascular plants. Cleef (1983) proposed that the floristic It is said, for instance, that the high altitude South interchange between North and South America American flora is largely derived from north increased little by little since the Miocene through temperate sources (Gentry 1982) and that many “Mesoamerican” islands and the Antilles; by the 2 Pliocene, with the elevation of mountains and the Table 1. Neotropical mosses common to North full closure of the Central American Isthmus, the and South America interchange also included holartic taxa that _____________________________________________ migrated to the Andean region. Range No. taxa The similarities between the moss floras of _____________________________________________ North and South America are well known. Because at the species level mosses follow patterns of CONTINUOUS distribution similar to those observed in the Central America (CA) 514 vascular plants, the hypotheses to account for CA, not in WI 162 their present ranges are essentially the same. The West Indies (WI) 393 high degree of community between the North and WI, not in CA 38 South America has already been explained in CA & WI 355 terms of migration through both Central America and the West Indies (Delgadillo 1992, 1993). DISCONTINUOUS However, the number of moss species participating Disjunct 118 in the interchange or the degree of community _________________________________________ between both land masses had not been determined TOTAL 675 accurately because of the lack of complete floristic _________________________________________ catalogues for the neotropical area; the number of Percent from total flora (675/4050)16.7 disjunct species had also remained undetermined. _________________________________________ We have recently compiled a data bank for neotropical mosses (LATMOSS) and have initiated a wider comparison of the North and change that has taken place between North and South American moss floras. The coverage and South America through these routes; the subject characteristics of LATMOSS was described was discussed by Delgadillo (1992, 1993) and elsewhere (Delgadillo 1992), but in this contribu- Schuster (1983) for bryophytes, and by contribu- tion its information is used to review the subject tors in Stehli and Webb (1985), for other organisms. of the floristic relationship between North and South America with emphasis on the origin of the The second group is of great phytogeogra- North-South American moss disjunction. phical interest for it comprises 118 disjunct moss taxa, i.e. species known from stations in North and LATMOSS includes about 675 species South America, but not from intermediate areas in and varieties of neotropical mosses that are shared Central America or the West Indies. This pattern between North and South America. These can be is well documented in the plant kingdom and has placed into two groups according to their received ample consideration (e.g., Bray 1898, continental distribution, namely, those with a Campbell 1944, Raven 1963), although there is continuous range in the neotropics and the still controversy as to its mode of origin disjunct taxa (Table 1). The group of taxa with a (Daubenmire 1978); examples among vascular continuous range is the most important; it com- plants include species of Clarkia (Raven & Lewis prises 514 species widely represented in North, 1959), Prosopis (Good 1964) Larrea (Bray 1898), Central, South America and the West Indies. and many others (cf. Constance 1963, Raven Included is a group of 159 taxa that are known 1963). However, for mosses, it has received little from Central America, but not from the West consideration except to say that they may have Indies; among the 393 taxa represented in the become widespread in the Pleistocene by West Indies there are 38 unknown from Central mountain “hopping”, but disappeared from America. The presence of species distributed in Central America afterwards. Central America and the West Indies has been regarded as indicative of the intense biotic ex- LATMOSS lacks altitudinal information 3 for some mosses, but the remaining disjuncts is certainly responsible for the present distribu- generally have broad altitudinal ranges or are tion of mosses because of its direct or indirect distributed from above 1,000 m up to about 5,000 influence on continental climates in the neotro- m in elevation. This altitudinal distribution and pics; in Mexico, the elevation of the eastern their present ranges in South America suggest sierras favored the drier climates in the Mexican that the disjunct taxa became widespread after the Plateau thus restricting the advance of tropical uplift of the Andes in the Pliocene and that further lowland mosses into continental areas of nor- upward and downward shifts during the thern Mexico. Rain shadows, easily observed in Pleistocene increased floristic interchange with the state of Puebla and elsewhere along the the displacement of vegetational belts. However, Neovolcanic Belt of Mexico, developed with the climatic fluctuation may have also eliminated uplift of mountain ranges. The drier climates of certain taxa from the Central American flora. western Central America and northern South America combined with the late uplift of the According to Janssens and Zander (1980), southern Central American mountains may have the disjunctive patterns in North America may modified moss ranges producing disjunct pat- have resulted from mid-Tertiary ranges that broke terns of many species. However, while this up following tectonic and climatological changes. contention may be acceptable for Central Ameri- Leptodontium flexifolium -known today from ca, it does not account for the absence of other Mexico, Central and South America, and from moss species in the West Indies. stations in Arizona, New Mexico and North Carolina-, had a range that extended to the Yukon I have stated elsewhere (Delgadillo 1993a) area in the Quaternary, as shown by subfossil that the archipelago condition of the Antilles, the samples collected in Canada (Janssens & Zander late elevation of the mountains and the climatic 1980). Subfossil material attributable to present- changes of the Pleistocene must have depleted day North-South American disjuncts has been the extant moss flora. It is likely that this loss reported from the Quaternary of North America resulted in disjunct ranges for species that were (cf. Janssens 1980, 1983; Miller 1980). Although unable to reenter the islands while, at the same fossil evidence is scanty, the distribution in Africa time, produced a high degree of floristic similarity of many disjunct mosses suggests ancient links between islands and continent as floristic with pre-Tertiary floras and wider ranges in periods replenishment could only come from continental of warm and equable climate during the Tertiary. sources. Zanten (1978) seems to think that because of the downward shift of vegetational belts, it may have Although most neotropical mosses exhi- been easier for cool-temperate taxa to migrate biting the North-South American disjunction are though Central America in glacial times. Thus, mainly distributed along the Andes, there are whether Tertiary or Pleistocene in age, it is several species whose continental distribution theoretically possible that the disjunct includes North America and Brazil,

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