Amphi-Pacific tropical disjunctions in the bryophyte floras of Asia and the New World

Abstract

Disjunctions between tropical America and tropical Asia, commonly called amphi-Pacific tropical disjunctions, have frequently been discussed among flowering plants but have received very little attention in bryology. A screening of the literature revealed nine species and sixteen genera or infrageneric taxa of bryophytes with amphi-Pacific tropical (or subtropical) ranges. They include Austinia tenuinervis, Diphyscium chiapense, D. longiflorum, Elmerobryum, Fissidens sect. Sarawakia, Ganguleea angulosa, Hydrogonium arcuatum, Hymenostyliella, Hymenostylium aurantiacum, Luisierella barbula, Mniomalia, Rozea, Sphaerotheciella and Sorapilla among the mosses and Ceratolejeunea grandiloba, Drepanolejeunea subg. Rhaphidolejeunea, Lejeunea sect. Echinocolea, Lobatiriccardia, Myriocoleopsis sect. Myriocoleopsis, Phycolepidozia, Pictolejeunea, Rectolejeunea, Southbya organensis and Vitalianthus among liverworts. All of them occur in tropical or subtropical Asia and the Neotropics but are not known from Africa. The causes of the amphi-Pacific tropical disjunctions in bryophytes are still unclear. In flowering plants, molecular analyses indicate that amphi-Pacific tropical ranges frequently resulted from past migration across Eurasia and the northern Atlantic Ocean, followed by local extinction. This scenario may also have operated in amphi-Pacific bryophytes but some might have reached South America via the southern Pacific migration route. The possibility of direct long-range dispersal across the Pacific Ocean cannot be ruled out and this scenario seems likely for Southbya organensis, which occurs on Hawaii and freely produces spores and small gemmae. The possibility that the disjunctive ranges reflect insufficient collecting and that some taxa also occur in Africa should also be taken into account. There is no strong evidence for human introduction of amphi-Pacific tropical bryophytes. The new combinations Lejeunea sect. Echinocolea (R.M.Schust.) Gradst. comb. nov. and Myriocoleopsis sect. Protocolea (R.M.Schust.) Gradst. comb. nov. are proposed.