1. ELAEAGNACEAE Jussieu
Leila M. Shultz
William A. Varga
Shrubs or trees, polygamous or dioecious, terrestrial, armed or unarmed, clonal or not. Stems scurfy-pubescent, glabrate, or glabrescent [glabrous]. Leaves deciduous or evergreen, opposite or alternate, simple; stipules absent; petiolate or sessile; blade membranous or leathery, venation pinnate, margins entire, surfaces pubescent, covered with silver, yellow, or rust scales, or stellate trichomes (sometimes glabrous adaxially in Elaeagnus multiflora). Inflorescences axillary, racemes, spikes, umbels, or flowers paired or solitary; bracts absent. Pedicels present or absent. Flowers bisexual or unisexual, actinomorphic; perianth in 1 series, hypogynous; hypanthium ± tubular, sometimes constricted, accrescent to pistil; sepals 2 or 4, appearing as lobes on hypanthium, valvate, connate; petals 0; nectary disc well-developed or rudimentary; stamens 4 or 8, filaments adnate to hypanthium, relatively short; anthers basifixed or dorsifixed, dehiscing laterally, pollen colporate; pistil 1-carpellate; ovary superior, 1-locular; placentation basal; style 1, apical, slender; stigma 1, capitate or linear; ovule 1, anatropous, bitegmic. Fruits achenes, covered by persistent and, sometimes, fleshy base of hypanthium, appearing drupe- or berrylike. Seed 1 per fruit, oblong, ovoid, or ellipsoid; embryo axile and centric, nearly filling testa; endosperm scanty or absent.
Genera 3, species ca. 45 (3 genera, 9 species in the flora): North America, Europe, Asia, Australia.
All species of Elaeagnaceae have root nodules with nitrogen-fixing bacteria (Frankia). The capacity to fix nitrogen is advantageous to species colonizing disturbed habitats and may account, in part, for the occurrence of Russian olive (Elaeagnus angustifolia) as an invasive plant in parts of North America.
Some species of Elaeagnaceae that have been introduced into the horticulture trade have become weedy or problem exotics; see discussion under 1. Elaeagnus. Some species treated here have been reported as naturalized and caution should be used in selecting plants for landscape use; most Elaeagnaceae species have the potential to become weedy.
Phylogenetic trees based on chloroplast rbcL sequences group Elaeagnaceae and Rhamnaceae in the same clade (M. Clawson et al. 1998); no proposal has been made to combine the families. Some lines of evidence suggest a relationship with Rhamnaceae: wood anatomy and the presence of vestured pits (S. Jansen et al. 2000), DNA sequencing (J. E. Richardson et al. 2000), vegetative characteristics (R. F. Thorne 1992b), and the occurrence of nitrogen fixing symbioses in Elaeagnaceae and some Rhamnaceae, Rosaceae, and Ulmaceae (D. E. Soltis et al. 1995).
SELECTED REFERENCES Jansen, S., F. Piesschaert, and E. Smets. 2000. Wood anatomy of Elaeagnaceae, with comments on vestured pits, helical thickenings, and systematic relationships. Amer. J. Bot. 87: 20–28. Nelson, A. 1935. The Elaeagnaceae—A mono-generic family. Amer. J. Bot. 22: 681–683.