JUGLANDACEAE (walnut family)
Contributed by Alan Whittemore
Plants small to
large trees, monoecious. Leaves alternate, short- to moderately long-petiolate.
Leaf blades 1 time pinnately compound, the leaflets unlobed, pinnately veined,
the margins toothed. Stipules absent. Staminate and pistillate inflorescences
separate, with small bracts (and usually also minute bractlets) subtending and
sometimes partially fused with each other and/or to the flowers, the staminate
flowers in long, pendent, solitary or clustered catkins produced near the base
of the current-year’s growth, the pistillate flowers solitary or in very short
spikes produced near the tip of the current-year’s growth. Flowers
actinomorphic, imperfect, the pistillate ones epigynous. Staminate flowers with
the calyx absent or minutely 4-lobed; corolla absent; the stamens mostly 3–50,
with a short filament and the anther attached at its base. Pistillate flowers
with the calyx absent or minutely 4-lobed; corolla absent; stamens and
staminodes absent; the ovary inferior (but sometimes appearing naked in the
absence of a perianth), usually 2-locular toward the base but appearing
1-locular toward the tip, with 1 ovule, the placentation basal. Styles usually
2 (sometimes united basally), relatively stout and spreading, each with an
expanded stigmatic region along the upper side. Fruits nuts, enclosed in a
thick, fleshy to leathery or woody husk. About 8 genera, about 60 species,
North America to South America, Europe, Asia, Pacific Islands.
The Missouri
genera of this family all have large, oil-rich nuts that are an important food
for wildlife, and have been important food for humans in the past. Various
species are larval food plants for a variety of butterflies and moths,
including the banded hairstreak butterfly (Satyrium calanus (Hübner)),
walnut sphinx moth (Amorpha juglandis (J.E. Sm.)), luna moth (Actias
luna (L.)), various underwing moths (Catocala spp.), dagger moths (Acronicta
spp.), one-spotted variant moth (Hypagyrtis unipunctata (Haw.)), and
giant regal moth (Citheronia regalis (Fabr.)) (Heitzman and Heitzman,
1987; Kurz, 2003). The last of these produces the largest caterpillar in the
United States, the hickory horned devil, a fierce-looking green creature that
can grow to nearly 15 cm in length. Members of the Juglandaceae are among the
last trees to leaf out in the spring and among the first to lose their leaves
in autumn.