Ixora L.

Timothy M. A. Utteridge and Laura V. S. Jennings (2022). Trees of New Guinea. Kew Publishing. Royal Botanic Gardens, Kew

Distribution

A genus of c. 545 species distributed in the tropics and subtropics in the Americas, Africa and Indian Ocean through Asia to Australia and the Pacific; 36 species occur in New Guinea (34 are endemic) and four species are known from the Solomon Islands (all endemic). The genus is most species rich in Asia and is the second most species rich genus of Rubiaceae in Asia behind Psychotria. Ixora is found in a variety of habitats throughout its range, including low to middle altitude forests.

Morphology General Habit

Shrubs, trees or monocaul treelets to 10 m

Morphology General

Raphides absent

Morphology Leaves Stipules

Stipules connate at base, triangular to ovate or lanceolate, sometimes ±keeled, apex finely pointed persistent or not

Morphology Leaves

Leaves with articulated petiole bases, bacterial nodules and domatia absent. Inflorescences terminal, 1–many-flowered, congested or very lax, bracts and bracteoles present, triangular to lanceolate, leaf pair subtending inflorescence (?leafy bract pair) is reduced, branches articulate or not. Flowers bisexual, 4-merous; calyx tube short, lobes small, triangular to ovate; corolla contorted to the left in bud, white, whitish-brown, yellow, orange, pink or red, tube narrowly cylindrical, sometime hairy in throat, lobes reflexed or spreading at anthesis stamen filaments short or long, adnate to upper part of tube, anthers exserted; ovary 2-locular, 1 ovule per locule; style slender, exserted, stigma bifid

Morphology Reproductive morphology Fruits

Fruits subglobose to bilobed drupes, slightly laterally compressed, green ripening to bright red or black; seeds 2 per fruit (sometimes 1 by abortion), no hilar cavity.

Recognition

It is most likely to be confused with other terminal inflorescence genera such as Psychotria, and members of the Pavetteae but can be told apart by the articulated petiole base (easier to see in dry specimens) and distinctive finely pointed stipules with pointed, needle-like apex combined with the 4-merous flowers and/or bilobed fruit. The genus lacks both ribbed pyrenes (cf. Psychotria) and seeds with hilar cavities (cf. Pavetteae genera). The flowers can be white but are often brightly coloured and showy.

Rubiaceae, D.M.Bridson & B.Verdcourt. Flora Zambesiaca 5:3. 2003

Morphology General Habit

Shrubs or small trees.

Morphology Leaves

Leaves opposite or rarely ternate, subsessile or petiolate or rarely sessile; mostly entirely glabrous; domatia and bacterial nodules absent (a bacterium causes a leaf spot in some species); petioles articulate (i.e. a joint between stem and petiole is apparent).

Morphology Leaves Stipules

Stipule limb truncate to triangular, usually connate for most of the length, bearing a short or long cuspidate or aristate lobe, rarely pubescent inside.

Morphology Reproductive morphology Flowers

Flowers usually fragrant, hermaphrodite, 4(5)-merous, few to many in terminal sessile to long-pedunculate ± lax corymbs or rarely spherical heads; inflorescence branches frequently coloured, pedicels present or absent*; inflorescence-subtending leaves usually smaller and frequently differing in shape from the foliage leaves, but with a fully developed stipule; bracts stipule-like; bracteoles present or rarely absent.

Morphology Reproductive morphology Flowers Calyx

Calyx tube ovoid; limb short, truncate or more usually 4(5)-toothed, shortly lobed or occasionally with well developed lobes.

Morphology Reproductive morphology Flowers Corolla

Corolla white, yellow, pink or red, glabrous outside or rarely pilose; tube cylindrical, usually slender, only slightly widened at the throat, naked or somewhat bearded at throat; lobes contorted to the right in bud, spreading or reflexing, linear to ovate, much shorter than or occasionally equalling the tube in length.

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens attached at the mouth of the tube; anthers twisted when dehisced.

Morphology Reproductive morphology Flowers Gynoecium Pistil

Ovary small, 2-locular (rarely 4-locular outside Africa); placentas fleshy, attached to the top of the septum; ovules solitary, immersed in the placentas; style slender, equalling or slightly exceeding the corolla tube, glabrous or sometimes pilose; pollen presenter exserted, 2-lobed; mature lobes always completely separate, usually recurved, equalling or a little shorter than the anthers.

Morphology Reproductive morphology Fruits

Drupes spherical or 2-lobed, slightly fleshy or coriaceous, containing 1 or 2 pyrenes; pyrenes thin walled, 1-seeded; calyx limb persistent.

Morphology Reproductive morphology Seeds

Seeds 2, hemispherical, with a deep circular excavation on plane face, convex face sometimes with minute occasionally shiny protuberances.