14. Diapensiaceae Lindley
Guy L. Nesom
Perennial herbs or subshrubs, evergreen, rhizomatous and/or stems creeping and adventitiously rooted, sometimes taprooted, ecto- and endotrophically mycorrhizal. Stems erect to decumbent or prostrate. Leaves basal and cauline, alternate or opposite, simple; stipules absent; petiole present or absent; blade margins entire or dentate-serrate. Inflorescences terminal racemes or solitary flowers. Flowers bisexual; perianth and androecium hypogynous; sepals 5, connate proximally or distinct; petals 5, connate proximally or distinct; stamens 5, antisepalous or basally connate into ring, epipetalous, alternating with staminodes; anthers transversely or longitudinally dehiscent; staminodes absent or 5, scalelike or spatulate; pistils 1, 3-carpellate; ovary superior, 3-locular; placentation axile; ovules usually anatropous, sometimes axile, hemitropous, campylotropous, or amphitropous, bitegmic, tenuinucellate; styles 1, terminal; stigmas 1, slightly 3-lobed to unlobed and capitate [disciform]. Fruits capsular, dehiscence loculicidal. Seeds 10-30, brown, cylindric; embryo straight to curved; endosperm copious, fleshy.
Genera 5, species 14 (4 genera, 6 species in the flora): North America, Europe, Asia.
In addition to the four genera treated here, one other genus completes the family: Berneuxia Decaisne, with one species in the Sino-Himalayan Mountains. Diapensialapponica and its sister D. obovata, as a pair, are circumboreal in distribution; all of the other species of the family are narrowly distributed. A phylogenetic analysis based on morphology and molecular data from four genes (K. Rönblom and A. A. Anderberg 2002) indicated that Galax is sister to all other genera; Pyxidanthera is sister to the remaining genera at the next higher node; relationships among Berneuxia, Diapensia, and Shortia are unresolved. In this interpretation, the "inverted-eucamptodromous" venation pattern shared by Diapensia and Pyxidanthera (H. T. Murphy and J. W. Hardin 1976) was perhaps developed in parallel.
Leaves of Diapensia, Galax, and some Shortia species become reddish to purplish or orange-bronze (anthocyanic) in the fall and winter. The colored leaves of Galax are gathered in the fall for the florist trade. Leaves of all genera of Diapensiaceae sequester large amounts of aluminum (L. Schultz, pers. comm.), an unusual characteristic for temperate plants.
SELECTED REFERENCES Doonan, S. 1993. The Diapensia family. Bull. Amer. Rock Gard. Soc. 51: 97-106. Qin, H. N. and B. M. Bartholomew. 2005. Diapensiaceae. In: Wu Z. and P. H. Raven, eds. 1994+. Flora of China. 11+ vols. Beijing and St. Louis. Vol. 14, pp. 235-237. Rönblom, K. and A. A. Anderberg. 2002. Phylogeny of Diapensiaceae based on molecular data and morphology. Syst. Bot. 27: 383-395. Scott, P. J. 2004. Diapensiaceae. In: K. Kubitzki et al., eds. 1990+. The Families and Genera of Vascular Plants. 9+ vols. Berlin etc. Vol. 6, pp. 117-121. Scott, P. J. and R. T. Day. 1983. Diapensiaceae: A review of the taxonomy. Taxon 32: 417-423. Wood, C. E. Jr. and R. B. Channell. 1959. The Empetraceae and Diapensiaceae of the southeastern United States. J. Arnold Arbor. 40: 161-171. Xi, Y. Z. and Tang Y. C. 1990. Pollen morphology and phylogenetic relationships in the Diapensiaceae. Cathaya 2: 89-112.