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Published In: Species Plantarum 1: 110. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 12/30/2016)
Acceptance : Accepted
Project Data     (Last Modified On 6/9/2020)
Notes:

Ixora comprises shrubs and small trees found in tropical regions around the world, and is a relatively large genus among flowering plants with more than 500 species and wide morphological variation. This genus was studied recently with broad sampling and molecular data, and the studies found it to include several smaller genera that each had some unusual character but otherwise matched Ixora (Mouly et al., 2009 in Amer. J. Bot.). Based on these analyses the tribe Ixoreae was also narrowed in circumscription to include only Ixora (Mouly et al. in Ann. Missouri Bot. Gard.). Ixora is represented on all continents, but has centers of larger species diversity in Africa, southeast Asia, and the Pacific. This genus has never been reviewed as a whole, but some regional floristic treatments have been published as well as the recent exemplary monograph of Ixora in Africa by De Block (1998). The information on this web page pertains to the Neotropical species of Ixora. Recent genus descriptions and floristic treatments include those of De Block (1998), Chen et al. (2011), Lorence et al. (2012), and Taylor et al. (2004).

Ixora is characterized in the Neotropics by its shrub or small tree habit; triangular stipules that are interpetiolar or shortly united around the stem; sessile to petiolate, opposite or ternate, generally medium-sized leaves; terminal or apparently axillary, cymose to paniculiform or subcapitate inflorescences with small bracts; 4-merous homostylous flowers; salverform white, yellow, pink, or red corollas with the lobes convolute; two linear stigmas; and drupaceous fruits with two plano-convex pyrenes. Ixora lacks raphides in the tissues. The stipules are characteristically aristate, sometimes with the tips well developed. The bases of petioles or leaf attachments are articulated, and the inflorescence axes often also have articulations at branching points. De Block (1998) analyzed the inflorescence arrangement and development of Ixora in detail, and showed that the apparently axillary inflorescences are developmentally borne on reduced axillary branches and thus this position is secondary in this genus. The fruits are generally red to purple-black. Ixora has about 45-50 native species in the Neotropics. Generally only a few Ixora are species found in a given region; the Guianas and eastern Brazil are Neotropical centers of species diversity for the genus. Ixora was reviewed for northeastern South America in some detail by Steyermark (1967: 341-353), and recently treated floristically in areas with more than one native species by Taylor et al. (2004), Lorence et al. (2012), and Delprete (2007).

The flowers of Ixora are somewhat unusual in having secondary pollen presentation. These flowers are protandrous, and the anthers and stigmas are both exserted and intially held at the same level. The anthers are introrse, and they release their pollen not widely but onto the outside of the stigmas and/or style. The style then elongates so that the pollen is exposed above the anthers, so the pollinators pick it up not from the anthers directly but from this secondary position. After the pollen has been deposited on the outsides of the stigmas and/or below them, then the stigmas spread apart to expose their now-receptive surfaces. Several species of Ixora have ternate leaves, and/or sessile leaves that are rounded to cordulate at the base. Most species of Ixora are glabrous throughout, or have only short puerulous pubescence. The fruits characteristically turn red or purplish red during development, then black at maturity. The inflorescence bracts are sometimes fused in pairs to form structures similar to the calyculi of Coffea and Tricalysia (e.g., Ixora aluminicola).

Several Ixora species are widely cultivated as ornamentals, in particular in tropical and subtropical regions, in their original form and in various cultivated forms and perhaps hybrids. Ixora coccinea is perhaps the most commonly cultivated species, and Ixora casei, Ixora finlaysoniana, and Ixora chinensis are also frequently grown (and confused with each other). Most of the cultivated Ixora species are from Asia and the Pacific, the area least studied with the most yet most poorly understood species in this genus. Various names are in use for these cultivated species, with varied accuracy.

Ixora is similar to the Paleotropical genus Pavetta, and these have been frequently confused; however Pavetta is not all that closely related to Ixora (Bremer & Eriksson, 2009) and can be separated by its stigmas fused into a single structure that is shortly bidentate at the top. Ixora has also been confused with Psychotria, which however has raphides in its tissues and valvate corolla lobes. The description below applies mainly to the Neotropical species of Ixora.

Author: C.M. Taylor.
The content of this web page was last revised on 9 June 2020.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

 

Distribution: In the Neotropics, in wet to seasonal vegetation at lower elevations, from Guatemala and the Antilles to Bollivia and southeastern Brazil.
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Low shrubs to small trees, unarmed, terrestrial, without raphides in the tissues. Leaves opposite or occasionally ternate, sessile to petiolate, entire, with higher-order venation not lineolate but sometimes the secondary and tertiary venation not well differentiated, without domatia; stipules interpetiolar and sometimes fused around the stem, triangular and often aristate, generally imbricated in bud, persistent or caducous. Inflorescences terminal or sometimes borne on short-shoots and apparently axillary, cymose to thyrsiform or reduced, 1-multiflowered, pedunculate to subsessile and frequently subtended by one or more nodes with stipules but without leaves, bracts developed, often fused in pairs especially subtending flowers. Flowers sessile to pedicellate, bisexual, homostylous, protandrous, fragrant, diurnal; hypanthia ellipsoid and sometimes flattened; calyx limb reduced to developed, subtruncate to 4-lobed, without calycophylls; corolla salverform, white to pink, red, yelllow or orange, internally glabrous or sometimes pubescent in throat, lobes 4, triangular, convolute in bud, without appendages; stamens 4, inserted in corolla throat, anthers ellipsoid to oblong, dorsifixed in basal portion, opening by linear slits, sometimes with apical appendage, exserted; ovary incompletely 2-locular, with ovules 1 in each locule, axile; stigmas 2, linear, exserted. Fruits drupaceous, subglobose to ellipsoid, juicy sometimes with leathery exocart, at maturity dark red to purple or black, with calyx limb persistent; pyrenes 2, hemispherical, bony or cartilaginous, whether dehiscent by preformed slits unknown; seeds 1 per pyrene, ellipsoid.

 

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