Tropicos | Name - !!Uncaria Schreb.

!!Uncaria Schreb.

Search in Index Nominum Genericorum (ING)

Search in African Plants Database at Geneva Botanical Garden

African Plants, Senckenberg Photo Gallery

Project Name Data (Last Modified On 6/27/2020)

Acceptance : Accepted

Note : Tribe Naucleeae

Project Data (Last Modified On 9/15/2020)

Notes :

Uncaria is characterized by its climbing habit that attaches to its support with distinctive, paired, recurved spines, stipules that are flattened and erect in bud, distinctive inflorescences with one to several subglobose heads, four-merous flowers with slender white corollas, capitate stigmas that are exserted on well developed styles, somewhat small capsular fruits, and winged flattened seeds. The plants often climb to the forest canopy. The growth form and its developmental sequence of Uncaria were described and illustrated in in detail in the excellent study of Ridsdale (1978: 44-45, fig. 1). The stipules are characteristically ovate to ligulate and reflexed athe lower nodes along the stem.

The paired spines are about 1-2 cm long and range from weakly curved to markedly spiralled, and are distinctive for Uncaria. These are borne in the axils of the leaves and have been various considered to correspond developmentally to reduced axillary shoots (Ridsdale 1978) or modified inflorescence peduncles (e.g., Taylor et al. 2004). There is no exact separation morphologically between an axillary short-shoot bearing an inflorescence and a peduncle, but Uncaria does not normally produce axillary short-shoots while these spines not infrequently produce one or several flowers at the tip. Thus, regarding these as peduncles has some justification. These are called "spines" based on long-term Rubiaceae usage, although morphologically they correspond to thorns (i.e., modified stems or shoot systems).

The globose inflorescences of Uncaria are also distinctive, especially when the flowers are open and the long styles are exserted. Bracts are often developed on the inflorescence branches but sometimes reduced in the flower heads, and the flower heads are sometimes enclosed by larger, caducous, stipuliform or foliaceous bracts. Secondary pollen presentation has been documented in the Asian species Uncaria rhynchophylla (Funamoto & Sugiera, 2016), in which the pollen is deposited on the outside of the stigma before that becomes receptive and the stigma form is similar to that documented in Cephalanthus occidentalis (Imbert & Richards 1999). Funamoto & Sugiura also documented nocturnal pollination in that one species; the floral biology and pollination of the Neotropical species do not seem to have been studied beyond one documentation that the flowers are pollinated (or visited?) by butterflies (Dulman, 2001).

Ridsdale (1978) described the corolla lobes of Uncaria as valvate to thinly imbricated in bud, and his description of these as valvate has been cited by later authors (Taylor et al., 2004; Lorence et al., 2012) but his description of these as thinly imbricated may be more often accurate. The capsules of Uncaria were inaccurately described as loculicidal by Chen & Taylor (2011). The arrangement of the flowers and fruit, whether sessile or pedicellate, is taxonomically important; however, the pedicels usually elongate shortly before the flowers open and then continue to elongate as the fruit develop, often markedly, so the pedicel length at anthesis may be difficult to discern from inflorescences in bud.

Uncaria has been variously classified as to tribe, initially (Schumann, 1891) and then again in the 21st century in Naucleeae (Razafimandimbison & Bremer, 2002), but in the 20th century for a time it was included in Cinchoneae (Bremekamp, 1966, Ridsdale, 1978) based on its placentas with ascending imbricated ovules and capsular fruits with flattened winged seeds. Since then, the circumscription of Cinchoneae has been deeply revised and narrowed based on molecular and morphological data (Andersson, 1995), with many of the genera included by Bremekamp now excluded and the Mitragyninae returned to Naucleeae. .

Uncaria tomentosa (along with other Rubiaeae) has been reported to have anti-cancer properties, and it and Uncaria guianensis are occasionally cultivated and commonly wild-collected as medical remedies by modern people as well as for traditional medicine with, presumably, some effect on natural populations. These medical claims and the secondary chemistry of these species have been studied scientifically to a limited degree, as detailed by Honório et al. (2016). Uncaria is widely considered medicinally useful also in Asia, with uses ranging from general tonics to supposedly curing HIV-AIDS, with various parts of the plants used and the materials generally wild-collected. Uncaria gambir, found from the Malay Peninsula through Borneo, is apparently both cultivated and wild-harvested as the source of gambir or gambier (Ridsdale, 1978, a yellowish dry resin chewed together with the betel nut and sometimes used in tanning.

Uncaria is similar to Sabicea, which also incudes twining climbers with similarly broad, reflexed stipules, but Sabicea lacks spines and has fleshy or juicy, baccate fruits. The two Neotropical species of Uncaria are Uncaria tomentosa and Uncaria guianensis, which were illustrated together by Taylor et al. (2004: 845, figs. 657, 658). Ridsdale's (1978) foundational monograph of Asian Uncaria was recently reviewed and updated by Turner (2018), with a focus on the species and literature of the Malayan Peninsular region.

Author: C.M. Taylor.
The content of this web page was last revised on 15 September 2020.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

Distribution : ca. 35 species across the tropics in humid to wet forest, generally at lower elevations; 2 species in the Neotropics, from northern Central America to Bolivia and Brazil; 1 species in Africa and Madagasar; and the center of diversity in southeastern Asia, Australia, and the western Pacific region.

References :