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The families of flowering plants

L. Watson and M.J. Dallwitz

Pyrolaceae Dum.

~ Ericaceae.

Including Pirolaceae auctt.; excluding Monotropaceae.

Habit and leaf form. Herbs. ‘Normal’ plants (mostly), or switch-plants. Leaves well developed (usually), or much reduced. Plants autotrophic, or parasitic (?); mycoheterotrophic (?); green and photosynthesizing; parasitic if parasitic, on roots of the host. Perennial; with a basal aggregation of leaves (often), or without conspicuous aggregations of leaves; sympodially rhizomatous. Leaves unless much reduced, persistent; alternate, or opposite, or whorled; flat; petiolate; non-sheathing; simple; epulvinate. Lamina entire; one-veined, or pinnately veined (unless much reduced). Leaves exstipulate. Lamina margins entire, or crenate, or serrate, or dentate. Leaf development not ‘graminaceous’.

Leaf anatomy. Minor leaf veins without phloem transfer cells (Pyrola).

Axial (stem, wood) anatomy. Nodes unilacunar. Secondary thickening absent, or developing from a conventional cambial ring (?). The axial xylem with vessels, or without vessels (?).

Reproductive type, pollination. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers solitary (Moneses), or aggregated in ‘inflorescences’; when aggrega, in racemes, or in umbels, or in corymbs. The ultimate inflorescence units racemose (Pyrola), or cymose. Inflorescences scapiflorous, or not scapiflorous. Flowers bracteate; ebracteolate; small; regular; (4–)5 merous; cyclic; pentacyclic. Free hypanthium absent. Hypogynous disk present, or absent; when present, intrastaminal; of separate members, or annular.

Perianth with distinct calyx and corolla; 8, or 0; 2 whorled; isomerous. Calyx (4–)5; 1 whorled; polysepalous, or gamosepalous (shortly, basally). Calyx lobes markedly longer than the tube. Calyx regular; persistent; imbricate; with the median member posterior. Corolla (4–)5; 1 whorled; polypetalous (though the primordium annular); imbricate; regular; white, or pink, or purple (or rose). Petals orbicular, sessile.

Androecium 8, or 10. Androecial members free of the perianth; free of one another; 2 whorled. Androecium exclusively of fertile stamens. Stamens 8, or 10; diplostemonous; alternisepalous; both alternating with and opposite the corolla members. Anthers becoming inverted during development, their morphological bases ostensibly apical in the mature stamens; dehiscing via pores (these ostensibly apical); introrse; tetrasporangiate; appendaged (the thecae produced into short tubes), or unappendaged. The anther appendages ostensibly apical. Anther wall initially with one middle layer. Tapetum glandular. Pollen shed in aggregates (nearly always), or shed as single grains; in tetrads (except in Orthilia). Pollen grains aperturate; 3 aperturate; colporate; 2-celled (in Chimaphila and Orthilia).

Gynoecium (4–)5 carpelled (opposite the petals). Carpels isomerous with the perianth. The pistil (4–)5 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary ostensibly (4–)5 locular (except towards the top). The ‘odd’ carpel anterior. Ovary sessile. Gynoecium stylate. Styles 1; attenuate from the ovary, or from a depression at the top of the ovary; apical; shorter than the ovary to much longer than the ovary (often declinate). Stylar canal present. Stigmas 1; (4–)5 lobed; capitate to peltate. Placentation axile (ostensibly), or parietal (i.e. the greatly intruded placentas not joined in the middle). Ovules 20–50 per locule (i.e. ‘many’); funicled; anatropous; unitegmic; tenuinucellate. Endothelium differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3 (uninucleate); not proliferating. Synergids slender, with broad bases. Endosperm formation cellular. Endosperm haustoria present; chalazal and micropylar (short, 1–celled). Embryogeny caryophyllad.

Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Seeds endospermic; minute, or small; winged (at each end). Embryo rudimentary at the time of seed release. Embryo achlorophyllous (1/1).

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. Sugars transported as oligosaccharides + sucrose. Cyanogenic, or not cyanogenic. Arbutin present. Iridoids detected; ‘Route I’ type (?normal). Proanthocyanidins present; cyanidin. Flavonols present; kaempferol and quercetin. Ellagic acid absent (one Pyrola species). Ursolic acid present.

Geography, cytology. Holarctic and Neotropical. Frigid zone and temperate (cold), sub-tropical to tropical (a few only). Cold North temperate and Arctic, Chimaphila extending to Central America and the West Indies. X = 8, 11, 13, 16, 19, 23.

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 30. Genera 4; Chimaphila, Moneses, Orthilia, Pyrola.

General remarks. Closely related to Ericaceae sensu stricto (q.v.): apart from differences among 'esoteric characters’ relying on limited sampling (caryophyllad embryogeny, seed with rudimentary embryo, no andromedotoxin), the compiled descriptions differ absolutely only in the herbaceous habit and ebracteolate flowers.

Illustrations. • Le Maout and Decaisne: Pyrola minor. • Moneses uniflora (as Pyrola uniflora): Eng. Bot. 900 (1866). • Orthilia secunda (as Pyrola secunda): Eng. Bot. 899 (1866). • Pyrola media (B. Ent.). • Pyrola media: Eng. Bot. 897 (1866). • Pyrola minor (B. Ent.). • Pyrola minor: Eng. Bot. 898 (1866).

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.’.