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The families of flowering plants

L. Watson and M.J. Dallwitz

Monotropaceae Nutt.

~ Ericaceae, Pyrolaceae.

Including Hypopitydaceae Link

Habit and leaf form. Herbs. More or less ‘normal’ plants. Leaves much reduced. Plants more or less succulent to non-succulent; parasitic; mycoheterotrophic; not green; parasitic on roots of the host. Perennial; without conspicuous aggregations of leaves; rhizomatous. Mesophytic. Leaves small; alternate; spiral; membranous; sessile; non-sheathing; simple; epulvinate. Lamina entire; with greatly reduced vascular tissue. Leaves exstipulate. Lamina margins entire.

Leaf anatomy. Stomata present, or absent; when present, mainly confined to one surface (abaxial). Hairs present; eglandular and glandular; unicellular and multicellular (with unicellular non-glandular, and stalked and shaggy glandular forms recorded).

Axial (stem, wood) anatomy. Nodes unilacunar. Primary vascular tissues in a cylinder, without separate bundles, or comprising a ring of bundles; collateral. Secondary thickening absent, or developing from a conventional cambial ring (if present, slight: the vascular system always reduced, variously comprising a ring of closed bundles embedded in prosenchymtous ground tissue or with or without a sheath of fibres). The axial xylem without vessels.

The axial xylem with tracheids.

Reproductive type, pollination. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in cymes, or in racemes. The ultimate inflorescence units cymose, or racemose. Inflorescences racemes, thyrses or heads; with involucral bracts, or without involucral bracts. Flowers bracteate; small to medium-sized; regular; cyclic; tetracyclic, or pentacyclic. Free hypanthium absent. Hypogynous disk present; intrastaminal; lobed.

Perianth with distinct calyx and corolla (usually), or sepaline (corolla rarely absent); 4–12; 2 whorled (usually), or 1 whorled; isomerous. Calyx (2–)4–5(–6) (sometimes not clearly distinguishable from bracts); 1 whorled; polysepalous, or gamosepalous (sometimes basally connate). Calyx lobes markedly longer than the tube. Calyx regular; imbricate. Corolla when present, (3–)5(–6); 1 whorled; polypetalous, or gamopetalous; imbricate, or contorted; regular.

Androecium 6–12 (often twice C). Androecial members free of the perianth; free of one another, or coherent (the filaments sometimes basally connate); when connate, 1 adelphous; 1 whorled, or 2 whorled. Androecium exclusively of fertile stamens. Stamens 6–12; diplostemonous (often), or isomerous with the perianth. Anthers becoming inverted during development, their morphological bases ostensibly apical in the mature stamens; dehiscing via pores to dehiscing via short slits (often), or dehiscing via longitudinal slits, or dehiscing transversely; finally introrse (inverting during development); unilocular (when transversely dehiscent), or bilocular; tetrasporangiate. Endothecium not developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads isobilateral, or decussate. Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate; (2–)3–4(–5) aperturate; colpate, or colporate (col(por)oidate, occasionally rupate); 2-celled (in 5 genera).

Gynoecium (4–)5(–6) carpelled. The pistil 1 celled, or (4–)5(–6) celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary (4–)5(–6) locular, or 1 locular. Gynoecium stylate. Styles 1; apical. Stylar canal present. Stigmas 1; capitate. Placentation when unilocular, parietal; axile, or parietal (when the placentas fall short of the middle). Ovules in the single cavity (when unilocular) 12–100 (‘many’); 12–50 per locule (‘many’); non-arillate; anatropous; unitegmic; tenuinucellate. Embryo-sac development Polygonum-type, or Allium-type. Antipodal cells formed; 3; not proliferating; persistent. Endosperm formation cellular. Endosperm haustoria present; chalazal and micropylar. Embryogeny caryophyllad.

Fruit fleshy, or non-fleshy; dehiscent, or indehiscent; a capsule (usually), or a berry. Capsules loculicidal. Fruit 20–100 seeded (‘many’). Seeds endospermic. Perisperm absent. Seeds minute. Embryo rudimentary at the time of seed release. Embryo achlorophyllous (1/1).

Physiology, phytochemistry. Sugars transported as oligosaccharides + sucrose. Not cyanogenic. Arbutin present. Iridoids detected; ‘Route I’ type (normal?). Ellagic acid absent. Andromedotoxin recorded.

Geography, cytology. Temperate (and tropical mountains). Widespread, temperate and tropical mountains. X = 8.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Corniflorae; Ericales. Cronquist’s Subclass Dilleniidae; Ericales. APG III core angiosperms; core eudicot; Superorder Asteranae. APG IV Order Ericales (as a synonym of Ericaceae).

Species 15. Genera 10; Allotropa, Cheilotheca, Hemitomes, Monotropa, Monotropastrum, Monotropsis, Pityopus, Pleuricospora, Pterospora, Sarcodes.

General remarks. Readily distinguishable, but legitimately interpreted as a herbaceous, mycoheterotrophic segregate of Ericaceae.

Illustrations. • Le Maout and Decaisne: Hypopitys, ~ Monotropa. • Monotropa hypopitys: B. Ent. 726. • Monotropa hypopitys: Eng. Bot. 901, 1866. • Cheilotheca malayana: Hutchinson.

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: 15th April 2018.’.