| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Apostasiaceae Bl.

~ Orchidaceae-Apostasioideae.

Including Neuwiediaceae (Burns-Balogh & Funk) R. Dahlgren ex Reveal & Hoogland

Habit and leaf form. Herbs. Plants autotrophic to parasitic; mycoheterotrophic. Without conspicuous aggregations of leaves. Leaves simple. Lamina entire; lanceolate; parallel-veined; without cross-venules. Vernation plicate.

General anatomy. Plants with silica bodies (these in idioblasts (stegmata) occurring along the fibres surrounding the vascular bundles).

Leaf anatomy. Epidermis without silica bodies. Stomata present; tetracytic, or anomocytic and tetracytic. Hairs absent. The mesophyll containing crystals. The crystals raphides. Foliar vessels absent.

Axial (stem, wood) anatomy. Primary vascular tissues consisting of scattered bundles; collateral. Secondary thickening absent. The axial xylem without vessels.

Root anatomy. Roots with velamen. Root xylem with vessels; vessel end-walls scalariform and simple (mainly simple).

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. The ultimate inflorescence units racemose. Inflorescences scapiflorous; racemes, sometimes branched. Flowers somewhat irregular to very irregular; more or less zygomorphic; resupinate (Neuwiedia), or not resupinate (Apostasia). The floral irregularity involving the perianth and involving the androecium (more consistently the latter). Flowers 3 merous; cyclic; supposedly basically pentacyclic. Perigone tube absent.

Perianth of ‘tepals’; 6 (3+3); free; 2 whorled (the median inner member sometimes larger, forming a labellum); isomerous; petaloid; white, or yellow. Tepal apex trichomes (TAT) absent (Apostasia, Neuwiedia).

Androecium 2–3 (the median of the outer whorl, which is sometimes missing, and the two laterals of the inner whorl). Androecial members free of the perianth; partially united with the gynoecium; coherent (at the base, and with the style); theoretically 2 whorled, or 1 whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes when present, 1 (the median member); external to the fertile stamens. Stamens 2, or 3; isomerous with the perianth; alterniperianthial (when the median of the outer whorl is present), or oppositiperianthial (when only the two laterals of the inner whorl are present); filantherous to with sessile anthers. Anthers dorsifixed to basifixed; dehiscing via longitudinal slits; introrse. The endothecial thickenings spiral. Microsporogenesis simultaneous. Pollen shed as single grains. Pollen grains aperturate; 1 aperturate; sulcate (operculate).

Gynoecium 3 carpelled. Carpels isomerous with the perianth. The pistil 3 celled. Gynoecium syncarpous; eu-syncarpous; inferior. Ovary 3 locular. The ‘odd’ carpel anterior. Styles 1. Stigmas 1; 2–3 lobed; capitate. Placentation axile. Ovules 10–50 per locule (i.e. ‘many’); anatropous.

Fruit fleshy, or non-fleshy; indehiscent (disintegrating, usually), or dehiscent; a capsule. Capsules when dehiscent, loculicidal (Neuwiedia). Fruit 30–100 seeded (‘many’). Seeds minute. Embryo rudimentary at the time of seed release, or weakly differentiated. Testa without phytomelan; hyaline.

Seedling. Seed germination resulting first in development of an endomycorrhizal 'protocorm'. Seedling collar not conspicuous. Coleoptile absent. Primary root ephemeral.

Geography, cytology. Tropical. S.E. Asia, Indomalaya, tropical Australia.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Liliiflorae; Orchidales. APG III core angiosperms; Superorder Lilianae; non-commelinid Monocot. APG IV Order Asparagales (as a synonym of Orchidaceae).

Species 20. Genera 2–3; Apostasia (including Adactylus), Neuwiedia.

General remarks. Evidently close to Orchidaceae sensu stricto, with the orchidaceous endomycorrhizal protocorm, but recorded as differing in absence of foliar vessels, as well as more conspicuously so in details of the androecium (2–3 fertile stamens with a single staminode external to them) and the 3-locular ovary.

Illustrations. • Apostasia and Neuwiedia spp.: Rolfe, J. Bot. Linn. Soc. (1890). • Neuwiedia veratrifolia, as N. lindleyi: Curtis Bot. Mag. 120 (1894). • Neuwiedia veratrifolia: Hook. Ic. Pl. 20 (1891). • Apostasia odorata: Lindley. • Floral diagrams (Apostasia, Neuwiedia).

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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