The families of flowering plants

L. Watson and M.J. Dallwitz

Parnassiaceae S.F. Gray

~ Celastraceae, Saxifragaceae.

Excluding Lepuropetalaceae.

Habit and leaf form. Herbs. Perennial; with a basal aggregation of leaves. Helophytic, or mesophytic. Leaves alternate; spiral; flat; long petiolate; non-sheathing; simple. Lamina entire; oblong, or ovate, or orbicular (or reniform); palmately veined; cross-venulate; often more or less cordate. Leaves exstipulate. Lamina margins entire.

Leaf anatomy. Minor leaf veins without phloem transfer cells.

Axial (stem, wood) anatomy. Nodes with a single leaf trace. Secondary thickening absent, or anomalous (said to be “polystelic at the nodes” (cf. Metcalfe and Chalk 1950)).

Reproductive type, pollination. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the androecium (from the bases of the staminodes). Pollination entomophilous; mechanism conspicuously specialized (the flowers protandrous, the stamens dehiscing over the gynoecium in sequence before moving outwards. The staminodes secreting nectar below, branched candelabra-like above, the branches each with a glistening yellow tip which supposedly interests flies).

Inflorescence, floral, fruit and seed morphology. Flowers solitary (on a long peduncle); medium-sized; regular; 5 merous; cyclic; pentacyclic. Floral receptacle markedly hollowed (and united to the base of the ovary).

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous; regular; imbricate. Corolla 5; 1 whorled; polypetalous; imbricate; regular; white, or yellow; persistent. Petals fringed, or entire.

Androecium 10 (interpreting each staminode as one member). Androecial members branched (the staminodes perhaps representing bunches of stamens), or unbranched; free of the perianth; free of one another; 2 whorled. Androecium including staminodes. Staminodes 5 (opposite the petals); internal to the fertile stamens; petaloid to non-petaloid (clavate or cuneate, branched candelabra-like above into 3, 5, 7, 9 or 15 branches, each branch tipped by a glistening yellow knob). Stamens 5; isomerous with the perianth; oppositisepalous; both alternating with and opposite the corolla members. Anthers ventrifixed; versatile; dehiscing via longitudinal slits; extrorse; tetrasporangiate. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Pollen grains aperturate; 3 aperturate; colporate; 2-celled.

Gynoecium 3–4 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior to partly inferior. Ovary 1 locular; sessile (globose). Gynoecium non-stylate to stylate (the stigmas sessile or almost so). Styles when detectable, 1 (thick); apical; much shorter than the ovary. Stigmas 3–4; commissural; dry type; papillate; Group II type (B(i)). Placentation parietal (the placentae large, projecting). Ovules in the single cavity 25–100 (‘many’); anatropous; bitegmic; tenuinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; proliferating (to about 5 cells), or not proliferating. Synergids hooked (with filiform apparatus). Endosperm formation nuclear. Embryogeny asterad.

Fruit non-fleshy; dehiscent; a capsule (3–4 valved); many seeded. Seeds thinly endospermic, or non-endospermic; very small; winged. Embryo straight (cylindrical).

Physiology, phytochemistry. Not cyanogenic.

Geography, cytology. Holarctic. Temperate. Arctic and North temperate (chiefly in upland bogs), south to India.

Taxonomy. Subclass Dicotyledonae; Crassinucelli (? — ovule tenuinucellate but bitegmic, polypetalous, flowers regular). Dahlgren’s Superorder Theiflorae; Droserales. Cronquist’s Subclass Rosidae; Rosales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Celastrales (as a synonym of Celastraceae).

Species 50. Genera 1; only genus: Parnassia.

General remarks. Comparisons of these descriptions show conspicuous differences from Celastraceae sensu stricto (q.v.) in habit, leaf venation and stem anatomy, as well as numerous differences involving inflorescence, floral morphology (notably in the androecium and gynoecium) and embryogeny.

Quotations ‘The Grass of Parnassus hath heretofore been described by blinde men; I do not meane such as are blinde in their eyes, but in their understandings, for if this plant be a kind of grasse, then may the Butter-burre or Colte’s-foote be reckoned for grasses, as also all other plants whatsoever.’
(John Gerarde 1597, ‘Herball’)

Illustrations. • Technical details: Parnassia. • Parnassia palustris (B. Ent.). • Parnassia mysorensis, P. nubicola and P. wightiana: R. Wight (1840).

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: 13th March 2017.’.