Little Walnut

Specimens of Juglans microcarpa with larger leaflets (parenthetical numbers above) may result from introgression with J . major . These have sometimes been treated as J . microcarpa var. stewartii (I. M. Johnston) W. E. Manning, but W. E. Manning (1978) reported this variety only from Mexico. Intermediates between J . microcarpa and J . nigra (q.v.) are also known.

Shrubs or small trees , to 10 m. Bark medium gray, split into ± rough ridges. Twigs with distal edge of leaf scar notched, glabrous or bordered by poorly defined velvety zone; pith light to dark brown. Terminal buds globose to short-ovoid, not flattened, 3-5 mm. Leaves 12-29 cm; petiole 1-3(-4) cm. Leaflets 17-25, lanceolate or narrowly lanceolate, weakly to strongly falcate, 5.2-6.3(-9.6) × 0.8-1.1(-2.2) cm, margins entire or toothed, apex long-acuminate; surfaces abaxially with capitate-glandular hairs (sometimes becoming sparse late in season except along veins), often scattered scales, axils of proximal veins usually, not always, with prominent tufts of fasciculate hairs, adaxially with capitate-glandular hairs (late in season hairs sometimes becoming sparse except along veins); terminal leaflet usually small. Staminate catkins 3-7 cm; stamens 20-25(-35) per flower; pollen sacs 0.8-1 mm. Fruits 1-3, globose, 1.4-2.3 cm, smooth, with capitate-glandular hairs; nuts globose to depressed-globose, 1.1-1.7 cm, grooved, surface between grooves smooth.

Kans., N.Mex., Okla., Tex.; Mexico (Chihuahua, Coahuila, and Nuevo León).

Flowering spring (Mar-Apr[-Jun]).

Along creeks and rivers; 200-2000m.

Juglans rupestris Engelmann ex Torrey

little walnut
Texas walnut
Texas black walnut
dwarf walnut
river walnut
Mexican walnut
walnut
nogal
nogalillo
nogalito
namboca

Riparian woodlands dominated by little walnut host a diverse array of
animal life [7]. These areas form particularly good habitat for many
species of birds [7].

More info for the terms: fruit, indehiscent, monoecious, phreatophyte, shrub, tree

Little walnut grows as a large, many-trunked shrub or small, clumped,
spreading, low-branched tree [15]. Plants may grow from 20 to 50 feet
(6-15 m) in height [5,30,31]. The strongly scented trunk is gray to
dark brown and becomes deeply fissured with age [18,36]. Twigs are
slender, orange-reddish, gray-brown, or gray and pubescent [31,36].
Little walnut is a phreatophyte with a long taproot which allows the
plant to obtain water from the water table [30].

Alternate, odd-pinnately compound leaves are 8 to 12 inches (20-30 cm)
long [18,36]. The 7 to 25 narrowly ovate to lanceolate leaflets are
serrate with low teeth [5,36]. The leaf base is cuneate to rounded and
the apex acute [36]. The upper surface is dark yellow to green, dull
and glabrous [31,36]; the lower surface is somewhat paler [31]. Leaves
are glabrous at maturity and aromatic when crushed [5,36].

Little walnut is monoecious [31]. Slender staminate catkins develop on
the wood of the previous year [31]. Yellow-green pistillate flowers are
borne singly or in clusters in short terminal spikes on the current
year's growth [5,31]. Fruit is globose, 0.5 to 0.8 inch (1.2-2.0 cm) in
diameter, brownish, and glabrous with age [5,18]. The fruit is borne
singly or in clusters of two or three [31]. The indehiscent husk or
shell is dark brown, thick, and fibrous [5,18,31]. The hard, dark brown
nut of little walnut [31] is the smallest of all walnuts (Juglans spp.)
[20]. It is globose to ovoid [25], deeply grooved longitudinally, and
0.8 to 0.9 inch (2-2.3 cm) in diameter [31]. The kernel is sweet and
oily [36].

The variety stewartii is characterized by slightly larger fruit (0.8 to
1 inch (21-25 mm) in length) and broader leaflets (0.6 to 0.9 inch
(15-23 mm) wide) [26]. The Arizona walnut is morphologically similar
to little walnut, and identification may be difficult where both species
occur together [30].

Little walnut grows from southwestern Kansas through Oklahoma to central
New Mexico and Texas, south into northeastern Mexico [5,15,31]. In
Texas, little walnut grows from the valley of the Colorado River west to
the mountains of the Trans-Pecos [36]. The variety stewartii grows in
the Chisos Mountains of Texas and extends into Mexico [26].

More info for the terms: fire regime, grassland, seed, shrubland, shrubs

Little walnut is most commonly associated with riparian woodlands which
burn infrequently. These narrow canyon forests frequently contrast
strikingly with adjacent desert grassland or shrubland communities [8].
Evidence suggests that recurrent fires in the much drier desert
grassland types may have eliminated invading shrubs and trees [16].

Because of its affinity for moist sites, little walnut exhibits few
specific adaptations to fire. Reestablishment presumably occurs through
off-site seed.

FIRE REGIMES :
Find fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under
"Find FIRE REGIMES".

More info for the terms: cover, prescribed fire

Bock and Bock [4] report that prescribed fire is "difficult to manage
and potentially very destructive in established riparian woodlands of
the Southwest." These relatively rare and fragile areas provide
important food and cover for desert wildlife [28]. Because browse and
cover are often limited in these areas, burning is not generally
recommended [28].

More info on this topic.

More info for the term: phanerophyte

Phanerophyte

More info for the term: woodland

Little walnut grows along rocky streambottoms, in canyons and arroyos,
and on first terraces of dry river beds [30,36]. It is particularly
common in arroyos of the Chihuahuan Desert [21]. In southeastern New
Mexico, little walnut grows along waterways that extend from the
foothills out onto the plains [20]. This plant commonly dominates
narrow riparian forests, which are often characterized by steep
limestone walls, and various river edge or creek bottom communities
[35,38]. Many sites have relatively high moisture availability.
Moisture is generally obtained from flowing or ephemeral streams and
flash floods [14,30].

Plant associates: Common overstory associates of the Edwards Plateau of
Texas include pecan (Carya illinoensis), Texas persimmon (Diospyros
texana), netleaf hackberry (Celtis reticulata), and live oak (Quercus
virginiana) [38]. Species such as netleaf hackberry, cedar elm (Ulmus
crassifolia), and littleleaf sumac (Rhus microphylla) are particularly
common on drier sites [37]. Agarito (Mahonia trifoliolata), Ashe
juniper (Juniperus ashei), bald cypress (Taxodium distichum), American
sycamore (Platanus occidentalis), desert willow (Chilopsis linearis),
and Texas persimmon are common components of river edge or riparian
woodland communities [9,37,41].

Soils: Little walnut commonly grows on shallow calcareous or alluvial
soils [35,37]. On many sites streambottom habitats are characterized
by gravelly soils, coarse sand, or exposed boulders [9,14].

Climate: Little walnut grows in areas which receive less than 7 to 38
inches ( less than 18 cm-72 cm) of precipitation annually [8,37].

Elevation: Little walnut grows primarily in valleys at intermediate
elevations [26]. Generalized elevational ranges by geographic location
are as follows:

Location Elevation Authority

TX-NM 3,950 to 5,250 feet (1,200-1,600 m) Legner and Goeden 1987
NM-TX less than 5,200 feet (< 1,585 m) Cottle 1931

More info on this topic.

This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

66 Ashe juniper - redberry (Pinchot) juniper
67 Mohrs ("shin") oak
68 Mesquite
235 Cottonwood - willow
240 Arizona cypress

More info on this topic.

This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

FRES15 Oak - hickory
FRES21 Ponderosa pine
FRES28 Western hardwoods
FRES31 Shinnery
FRES32 Texas savanna

More info on this topic.

This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

K060 Mesquite savanna
K061 Mesquite - acacia savanna
K062 Mesquite - live oak savanna
K071 Shinnery
K084 Cross Timbers
K086 Juniper - oak savanna
K087 Mesquite - oak savanna

Little documentation exists on the specific effects of fire on little
walnut. Mature individuals of the closely related Arizona walnut are
reportedly killed by hot wildfires [4]. Portions of the stumps or root
collars of small black walnuts commonly survive fire [12].

Little walnut provides some deer browse in parts of New Mexico [19].
The nuts are a valuable food source for many wildlife species including
squirrels and other rodents [5,30,36]. The rock squirrel readily
consumes nuts when available [30].

More info for the term: woodland

Texas walnut occurs abundantly in a number of riparian woodland
communities. It is included as a dominant or indicator in the following
community type (cts) classifications:

Area Classification Authority

TX: Brewster Co. general veg. cts Carignan 1988

NM, TX: Guadalupe general veg. cts Gehlbach 1967
Escarpment

Southwest riparian cts Szaro 1990a

Southwest riparian cts Szaro 1990b

TX: Brewster Co. general veg. cts Denyes 1956

More info for the terms: shrub, tree

Tree, Shrub

More info for the term: fruit

Damage: The walnut husk fly infests ripening fruit of little walnut
after late summer rains [20]. The amount of fruit damaged by this
insect varies annually but generally tends to be less in exposed windy
areas [20]. Mature little walnut appears to be relatively unaffected by
even "devastating" flash floods [14].

Disease: Little walnut is highly susceptible to root or crown rot when
periodically flooded [24]. It is less susceptible to the fungus-caused
walnut anthracose than black walnut is [3].

The nut meat of little walnut is described as nutritious and of "high
quality" [30].

AZ KS NM OK TX MEXICO

More info for the terms: rootstock, tree

Little walnut plants are sometimes cultivated for the sweet, edible nuts
[17,30,31]. It is the primary rootstock used in Texas for trials of
nonnative walnuts and has potential value for use in developing walnut
cultivars [29]. It has been cultivated as an ornamental and shade tree
in both the United States and Europe [36]. Plants were first cultivated
in 1868 [5].

Nuts of little walnut are highly palatable to a wide variety of wildlife
species [5].

More info on this topic.

More info for the terms: fruit, seed, vines

Flowering begins with or slightly after leaf emergence [5]. Male and
female flowers, which are borne on the same trees, mature at different
times, thus promoting cross-pollination [5]. Fruit ripens in late
summer or fall [5]. Generalized flowering and fruiting dates for little
walnut by geographic location are as follows:

Location Flowering Fruit ripe Authority

SW March-April ---- Vines 1960
Great Plains March-April ---- Great Plains Flora Assoc. 1986
c Great Plains May October Stephens 1973

Seed is typically dispersed in fall [5]. Some fruit falls from the
trees before the last week of August [21], but in many areas, most seed
falls during September and October [1]. Timing of fruit fall depends
largely on weather conditions such as wind and rain [21].

More info for the terms: root collar, wildfire, woodland

The response of little walnut to fire has not been documented. Small
individuals of the closely related black walnut often sprout freely from
the stump after aboveground vegetation is killed or damaged by fire
[12]. Fowells [12] reports that sprouts which develop high on older
stumps often succumb to rot or decay, but those which develop from the
root collar generally survive. Larger individuals of the Arizona walnut
apparently did not sprout after a hot wildfire in a Southwestern
riparian woodland [4].

More info for the terms: caudex, root crown, seed

survivor species; surviving root crown or caudex
off-site colonizer; seed carried by animals or water; postfire yr 1&2

More info for the terms: natural, seed, stratification

Seed: Most walnuts bear abundant seed crops at irregular intervals
[12]. Little walnut first bears seed at approximately 20 years of age
[5]. Seed may be dispersed by animals or water.

Germination: The seeds of most walnuts are characterized by a dormant
embryo [40]. Seed dormancy can be broken by stratification at 34 to 41
degrees F (1-5 degrees C) for 90 to 120 days [5]. Stratified seed generally germinates within 4 weeks,
but much variation has been noted [5]. Under natural conditions, seeds
germinate in the spring [5]. Results of laboratory tests are as follows
[5]:

germination test conditions germination energy
daily temperature dur. amount days
days night (days) (percent)

86 68 30-60 68 14

Germination capacity has averaged 46 percent in greenhouse experiments
[5].

Seedling establishment: Once established, young plants generally grow rapidly [36].

Vegetative regeneration: Epicormic branching of walnuts has been
reported [6]. The closely related black walnut reportedly stump-sprouts
after trees are cut or killed by fire [12].

More info on this topic.

This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

7 Lower Basin and Range
13 Rocky Mountain Piedmont
14 Great Plains

More info on this topic.

More info for the terms: climax, woodland

Little walnut is largely restricted to drainageways which support
riparian woodland communities. These woodlands generally represent
climax or "postclimax" communities [8].

Juglans rupestris
Juglans nana

More info for the term: fruit

The currently accepted scientific name of little walnut is Juglans
microcarpa Berl. [17]. Two varieties are delineated on the basis of
morphological differences such as leaf and fruit size [26]. The
following varieties are commonly recognized [17]:

Juglans microcarpa var. microcarpa
Juglans microcarpa var. stewartii

Little walnut hybridizes with the closely related Arizona black walnut
(Juglans major) [36], and populations which exhibit various intermediate
characteristics have been reported [26]. At the eastern edge of its
range, little walnut intergrades with black walnut (J. nigra) [3,31].

More info for the term: seed

Little walnut has been widely used for shelterbelt plantings [6,38] and
has shown promise for use in some types of rehabilitation projects.
Under certain conditions, it can aid in soil stabilization [33]. Plants
can be easily propagated from seed. Cleaned seed averages 92 per pound
(203/ kg) [5]. Seed can be planted during the fall in sandy soils at
depths of 1 to 2 inches (3-5 cm) [36]. Methods of propagating by seed
have been examined in detail [5,36].

Wood of little walnut is dark brown, hard and heavy but not strong [36].
Sapwood is white [36]. Annual rings are poorly cemented and the wood
frequently comes apart as it is being worked [20]. This characteristic
limits its use [20]. However, wood is sometimes used to make cabinets,
furniture, paneling, and veneer [36].

Juglans microcarpa, known also as the little walnut, Texas walnut, Texas black walnut or little black walnut (as it belongs to the "black walnuts" section Juglans sect. Rhysocaryon), is a large shrub or small tree (10–30 ft tall) which grows wild along streams and ravines in Texas, New Mexico, Oklahoma, and Kansas, and the northernmost states of Mexico. It produces nuts with a width of 1/2—3/4 in. The pinnately compound leaves bear 7—25 untoothed to finely-toothed leaflets, each 1/4—1/2 in wide. It is found at elevations ranging from 700 ft to 6700 ft.

Two varieties are recognized: J. microcarpa var. microcarpa and J. microcarpa var. stewartii.

Where the range of J. microcarpa overlaps with J. major, the two species interbreed, producing populations with intermediate characteristics. This phenomenon has also been found where J. microcarpa trees grows near J. nigra trees.

Juglans (literally "Jupiter's acorn") is the Latin name of the walnut. Microcarpa means "having small fruit". Though very small, the seeds contained within the nuts are edible.