l - CNCFlora

Volume 91, Number 4
2004
Croat
Revision of Dieffenbachia 683
Costa Rica and Panama, but even these are not independently after the Andes began to arise towidespread
in the two countries. Those shared are ward the end of the Cretaceous (Raven & Axelrocl,
D. aurantiaca, D. beachiana, D. davidsei, D. gra- 1974). The fact that there are no truly wide-ranging
yumiana, D. killipii, D. nitidipetiolata, D. oerstedii, species, i.e., those ranging from Mexico to Brazil,
D. tonduzii, and D. wendlandii. Dieffenbachia au- attests to this isolation. The high rates of endemism
rantiaca occurs only in southwestern Costa Rica in in Costa Rica and Panama as well as Mexico perthe
vicinity of the Osa Peninsula and in adjacent haps reflects the isolation of these areas during pe-
Panama in the Burica Peninsula area (Fig. 27). riods when the oceans were at much higher levels
Both Dieffenbachia beachiana and D. grayumiana than they are today, and when the area that is now
range from northern Costa Rica to western Panama central Panama and Costa Rica was subsequently
(Bocas del Toro) (Figs. 28, 27), while D. daviclsei clisconnectecl from South America. At the close of
ranges from northwestern Costa Rica to central the Tertiary period, 18,000 years ago, the sea level
Panama (San Blas) and Colombia (Fig. 27). was about 100 m higher than today (Holmes, 1969).
A total of 11 species (42Wo of the total) of Dief- Much earlier the land mass of what is now Central
fenbachia are endemic to either Costa Rica or Pan- America began to emerge as a series of islands durama.
Endemism is particularly high in Panama ing the Oligocene epoch with further uplifting durwhere
8 of the 26 species (31Wo) are endemic. In ing the Middle Miocene. It was not until the Upper
Panama endemic species are D. copensis, D. cre- Miocene and Pliocene epochs that the final portions
bripistillata, D. fosteri, D. fortunensis, D. galclame- of the isthmus of Panama emerged above sea level
siae, D. Iutheri, D. panamensis, and D. pittieri (Figs. (Torre, 1965), and the final connection of Central
27-30). In Costa Rica 3 of 26 species (12Wo) are and South America was about 5.7 million years ago.
endemic. Costa Rican endemics are D. burgeri, D. To put these geological events in relation to the
hammelii, ancl D. horichii (Fig. 27). Neither Mexicc moclern aroicl flora, it should be notecl that even
nor Miclelle America have enclemic species. cluring this era preculsors to the extant flora proI)-
DiefJenbflchifl isthmia (Fig. 28), D. Iongisl)eltha ably alreacly existe(l. The angiosperm floras of the
(Fig. 29), and D. obscllrinervisl (Fig. 29) range Oligo(ene Wele Ivelieve(l to have consiste(! almost
ae X OSS the l sthmus of Panama from Vel aguas Prov- elltirely of extant genera and with existillg spee ies
inc e to northel ll Colombia. DieiZenbflc1lia aur(letifl- alllong Oligoe ene atl(l Plio( ene ftol as ('raklllajan,
a,19. beachiflnfl, and D. grflyllmiflnfl (Figs.27,28) 19G9).
ale the only s)ecies oc(urring in both Costa Rica Equally important as geo]ogy lo the isolcltion of
an(l Panama. S(lme spe( ies are fulther isolate({. tlle Celltlal Amelicall aroid flola are ecologi(al fac-
1)ieffenl)achia allrantiflc f1 an(1 1). burgeri are re- toI s fol Central Amel ic an spee ies of Dieffenl)achi(l.
stri( te(l to the legion of the ()sa Peninsula in south- Mue h of eastern Panama c onsists of bl oad expanses
western Costa Ric a (or in the ( ase of D. aurantiac of Tropical moist forest (T-mf) with other, generally
in Panama on the adjacent Burica Peninsula; Fig. smaller areas of Premontane wet (P-wf) and Tropical
27) and D. horichii is lestricted to a relatively small wet forest (T-mf) (Holdridge, 1967). In contrast to
area on the Pacific slope of Costa Rica (Fig. 27). Panama, much of the Choco area of northwestern
Several other species are also narrowly restricted Colombia consists of much wetter pluvial forest
or known only from the type specimen. Dieffen- with annual precipitation exceeding 11,700 mm
bachia fosteri is restricted to northeastern Panama (Gentry, 1982). This broad band of pluvial forest
(Fig. 27). Dieifenbachia fortunensis is restricted to with its own suite of unique endemic species no
the northern Chiriqui Province (Fig. 28). Dieffen- doubt acts as a dispersal barrier for species from
bachia copensis is found only in the Cocle Province regions with less rainfall. It may account for those
of Panama (Fig. 27), and D. galdamesiae in a small Panamanian and Costa Rican species that skip the
area south of the Panama Canal (Fig. 28). wettest areas of northwestern South America but re-
Further collecting in Colombia, especially along occur in the relatively drier areas of mesic western
the western slope of the Andes, may change the Ecuador.
distribution of Dieffenbachia7 but the current pat- Middle America has low species diversity with
terns most likely reflect the realities of life zone Guatemala having only two species and Honduras
ecology and geologic history of the area rather than three. Only Nicaragua, with six species, four of
under-collecting. Since relatively few species of Ar- them restricted to the southeastern corner near Cosaceae
are known to occur at lower elevations on ta Rica, is moderately rich in species. All except
both the eastern and western side of the Andes, it D. standleyi and D. wendlandii appear to range into
can be presumed that the evolution of the respec- the country from Costa Rica. The low species ditive
Amazonian and Pacific coastal floras occurred versity and very low aroid endemism in Dieffen-