Evolution of Rhaphithamnus venustus (Verbenaceae), A Gynodioecious Hummingbird-Pollinated Endemic of the Juan Fernandez Islands, Chile

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dc.contributor.author Sun, Byung Y.
dc.contributor.author Stuessy, Tod F.
dc.contributor.author Humana, Ana M.
dc.contributor.author Riveros G, Magaly
dc.contributor.author Crawford, Daniel J.
dc.date.accessioned 2008-09-21T02:09:45Z
dc.date.available 2008-09-21T02:09:45Z
dc.date.issued 1996-01
dc.description.abstract Rhaphithamnus Miers. (Verbenaceae) consists of two species restricted to southern South America. Rhaphithamnus spinosus (A. L. Juss.) Mold. occurs in mainland Chile and adjacent Argentina; R. venustus (philippi) Robinson is endemic to the two islands (Masatierra and Masafuera) of the Juan Fernandez Archipelago. Both species are related to Citharexylum Miller, a genus distributed from Peru northward along the Andes. Youthful geological ages of the Juan Fernandez Islands (1-4 myr) and occurrences of the sister group also on the con.tinent suggest that R. venustus evolved from R. spinosus rather than the reverse. Morphologically the two species differ primarily in corolla length and color and stem armament, with R. spinosus with shorter (ca. 12 mm) and bluish flowers and usually with axillary thorns in contrast to longer (ca. 25 mm) and purple flowers and lack of thorns for R. venustus. Studies of pollinators reveal bees, flies, beetles, and infrequently hummingbirds for R. spinosus and exclusively hummingbirds for R. venustus. Rhaphithamnus spinosus is hermaphroditic and partially self-compatible, whereas R. venustus is gynodioecious and with an unknown compatibility system. In the latter species female flowers appear to be in an early stage of evolution because anthers are still fully formed, but usually without pollen grains. Embryological studies reveal breakdown of pollen mother cells (and tapetal cells) during meiosis. We hypothesize that evolution of floral features in R. venustus is a result of a change from primarily insect to hummingbird pollination; loss of thorns may result from absence of herbivores in the Islands. Gynodioecy in Rhaphithamnus may have as its selective basis reduction of inbreeding depression otherwise brought on by geitonogamy in scattered individuals of small populations.
dc.identifier.citation Sun BY, Stuessy TF, Humana AM, Riveros GM, Crawford Daniel J. 1996. Evolution of Rhaphithamnus venustus (Verbenaceae), a gynodioecious hummingbird-pollinated endemic of the Juan Fernandez Islands, Chile. Pac Sci 50(1): 55-65.
dc.identifier.issn 0030-8870
dc.identifier.uri http://hdl.handle.net/10125/2586
dc.language.iso en-US
dc.publisher University of Hawaii Press
dc.title Evolution of Rhaphithamnus venustus (Verbenaceae), A Gynodioecious Hummingbird-Pollinated Endemic of the Juan Fernandez Islands, Chile
dc.type Article
dc.type.dcmi Text
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Pacific Science Volume 50, Number 1, 1996