| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Costaceae (K. Schum.) Nak.

~ Zingiberaceae.

Habit and leaf form. Herbs; without essential oils. Plants succulent to non-succulent; green and photosynthesizing. Perennial; rhizomatous. Self supporting, or epiphytic. Mesophytic. Leaves alternate; spiral, or four-ranked; ‘herbaceous’, or fleshy; petiolate, or sessile; sheathing. Leaf sheaths with joined margins. Leaves without marked odour (i.e., unlike Zingiberaceae); simple; epulvinate. Lamina entire; lanceolate to ovate; pinnately veined (‘pinnate-parallel’); without cross-venules. Leaves conspicuously ligulate. Lamina margins entire. Vernation convolute.

General anatomy. Plants with silica bodies (internal, stellate or druselike).

Leaf anatomy. Epidermis without differentiation into ‘long’ and ‘short’ cells; without silica bodies. Stomata present; paracytic, or tetracytic. Guard-cells not ‘grass type’. The mesophyll without etherial oil cells; not containing mucilage cells; containing crystals. The crystals druses, or solitary-prismatic (? — no raphides). Midrib conspicuous, or not conspicuous. Foliar vessels absent. Minor leaf veins without phloem transfer cells (Costus, Tarpeinocheilos).

Axial (stem, wood) anatomy. Cork cambium absent. Secondary thickening absent. The axial xylem with vessels, or without vessels.

The vessel end-walls scalariform.

Root anatomy. Root xylem with vessels; vessel end-walls scalariform.

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the gynoecium (from septal nectaries, often two well developed and one reduced). Pollination entomophilous, or chiropterophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’. The ultimate inflorescence units when flowers aggregated, cymose. Inflorescences terminal, or axillary. Flowers bracteate (the bracts with a linear extrafloral nectary beneath the tip); bracteolate, or ebracteolate; very irregular; zygomorphic. The floral irregularity involving the perianth and involving the androecium. Flowers basically 3 merous (but much modified); cyclic. Perigone tube absent.

Perianth with distinct calyx and corolla; 6; free; 2 whorled; isomerous; different in the two whorls. Calyx 3; 1 whorled; gamosepalous; blunt-lobed; unequal but not bilabiate (spathelike, or constituting a tube split to the base on one side); imbricate; with the median member anterior. Corolla 3; 1 whorled; gamopetalous; unequal but not bilabiate (the median lobe larger and often upcurved).

Androecium 1 (ostensibly), or 6 (theoretically, but scarcely recognisable as such). Androecial members free of the perianth; united with the gynoecium (in that the thin style is fused to a groove along the length of the single anther); markedly unequal; free of one another and coherent, or coherent (depending on interpretation); supposedly 2 whorled. Androecium including staminodes. Staminodes supposedly 5; petaloid. Stamens 1 (the median, posterior member of the theoretical inner whorl); reduced in number relative to the adjacent perianth; petaloid. Anthers adnate; non-versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Anther epidermis persistent. Microsporogenesis successive. Anther wall initially with more than one middle layer. Tapetum glandular. Pollen grains aperturate; 1 aperturate, or 5–16 aperturate; sulcate, or foraminate, or spiraperturate; 2-celled.

Gynoecium 3 carpelled. The pistil (1–)3 celled. Gynoecium syncarpous; eu-syncarpous; inferior. Ovary (1–)3 locular. Epigynous disk often present. Styles 1; apical. Stigmas 1; wet type; papillate; Group III type. Placentation when unilocular parietal; usually, when trilocular axile. Ovules 15–50 per locule (i.e. ‘many’); arillate; anatropous; bitegmic; crassinucellate. Outer integument not contributing to the micropyle. Embryo-sac development Adoxa-type. Polar nuclei fusing prior to fertilization. Antipodal cells not formed (the nuclei ephemeral). Synergids hooked. Hypostase present. Endosperm formation helobial. Embryogeny caryophyllad.

Fruit fleshy, or non-fleshy; dehiscent, or indehiscent; a capsule, or a nut, or capsular-indehiscent, or achene-like (?— ‘a capsule, or dry and indehiscent’). Seeds endospermic. Endosperm not oily (starchy). Perisperm present. Seeds with starch. Cotyledons 1. Embryo straight. Testa encrusted with phytomelan; black.

Seedling. Hypocotyl internode present (long). Seedling collar not conspicuous. Cotyledon hyperphyll compact (small); non-assimilatory (but borne atop the large, leaflike, assimilatory sheath). Coleoptile absent. First leaf dorsiventral. Primary root ephemeral.

Physiology, phytochemistry. Cyanogenic (Costus). Saponins/sapogenins present (Costus).

Geography, cytology. Tropical. Widespread tropical. X = 8, 9.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Zingiberiflorae; Zingiberales. APG III core angiosperms; Superorder Lilianae; commelinid Monocot. APG IV Order Zingiberales.

Species 200. Genera 5; Chamaecostus, Costus, Dimerocostus, Monocostus, Tapeinocheilos.

Economic uses, etc. Commonly grown as garden ornamentals in warm regions.

Illustrations. • Chamaecostus cuspidatus, as Costus igneus: Bot. Mag. 111 (1885). • Costus afer: Bot. Reg. 683, 1822. • Costus afer: Bot. Mag. 83 (1857). • Costus elegans (as C. malortieanus): Bot. Mag. 97 (1871). • Costus spectabilis, as Cadalvena dalzielii: Hook. Ic. Pl. 31 (1915). • Hellenia speciosa (as Costus): Bot. Reg. 665, 1822.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 8th June 2026. delta-intkey.com’.

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