Asteridae: Rubiales. The Rubiaceae are trees, shrubs, or infrequently herbs comprising about 450 genera and 6,500 species, including some lianous forms. The leaves are simple and usually entire, and are opposite or sometimes whorled; stipules are present and interpetiolar. The flowers are nearly always bisexual and actinomorphic, often heterostylous, and usually are in cymose inflorescences. The calyx is mostly somewhat reduced and 4-5-lobed or sometimes the lobes are obsolete or rarely one of them greatly expanded and brightly colored. The sympetalous corolla is mostly 4-5-lobed, occasionally with 3 or up to 10 lobes. The androecium consists of as many stamens as corolla lobes and is adnate to the corolla tube or epigynous zone, alternate with the lobes. The gynoecium consists of a single compound pistil of 2 or seldom more carpels, a single style, and a nearly always inferior ovary with the number of locules equaling the number of carpels, each with 1-many axile ovules. An epigynous nectary disk is usually present. The fruit is variable, sometimes forming multiples.
Each "thumbnail" image below is linked to a larger photograph.
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Morinda citrifolia, noni. Notice the opposite leaves and conspicuous interpetiolar stipules. Multiple fruits result from coalescence of the inferior ovaries of many closely packed flowers. | ||
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Spermacoce assurgens, buttonweed. This weedy species has 4-merous flowers. Note the tubular corolla and the small calyx teeth on the inferior ovary. | ||
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Pentas lanceolata. This photo shows three different color forms of this common ornamental shrub. Note the cymose clusters of 5-merous flowers. | ||
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Rondeletia amoena. This photo shows opposite leaves and one of the interpetiolar stipules. The matching stipule of the pair is out of view on the other side of the stem. | ||
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Gardenia taietensis, Tahitian gardenia. This is an example of the less frequent condition in the family where the number of corolla lobes and stamens exceeds 5. | ||
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Warscewiczia coccinea, wild poinsettia. This unusual species has one calyx lobe of one or two of the peripheral flowers in each cluster greatly enlarged and brightly colored. This is a type of loosely organized pseudanthium or cluster of flowers that mimics a single flower as the attraction unit for pollinators. Note the otherwise tiny calyx lobes, the tubular yellow corollas and the inferior ovaries. | ||
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Mussaenda sp. In this species the calyx lobes are greatly enlarged, producing an attractive unit more conspicuous than the corolla. | ||
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Ixora sp., ixora. Any of several shrubby ornamental species from tropical Asia, with red, white, yellow or pink flowers. | ||
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Nertera granadensis, makole. This small, creeping Hawaiian native is found in wet sites. Notice the 4-merous flowers and opposite leaves with interpetiolar stipules. | ||
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Coprosma ernodeoides, kukaenene. This Hawaiian native genus is unusual in the family because of its dioecious, wind pollinated species. This is a female plant (left photo). Notice the long, brush-like stigmas. The photo on the right shows a male plant with staminate flowers. | ||
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Galium sp., bedstraw. The bicarpellate nature of the fruit is readily apparent. |
