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Juglans microcarpa; photograph (c) Chet Burrier, some rights reserved (CC BY) CC BY(c) Chet Burrier, some rights reserved (CC BY) · observed growing wild · 2026-03-09

Juglans microcarpa Berland.

Little walnut; Texas walnut; River walnut; Little black walnut

Juglandaceae · Kansas, Oklahoma +3

Cited as Kew's World Checklist cites it, Juglans microcarpa Berland.: GBIF's backbone key for this page carries the name with another author, Berl.

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Juglans microcarpa, photograph (c) Sam Kieschnick, some rights reserved (CC BY)Juglans microcarpa, photograph (c) Sam Kieschnick, some rights reserved (CC BY)Juglans microcarpa, photograph author not stated, no rights reservedJuglans microcarpa, photograph author not stated, no rights reservedJuglans microcarpa, photograph (c) Chet Burrier, some rights reserved (CC BY)Juglans microcarpa, photograph (c) Chet Burrier, some rights reserved (CC BY) 62 photographs ›
Habitat figures
Cold floor (1 night in 100)
-5.1°C
Record low -15.4 °C in 44 years, at a typical spot in the range NASA POWER
Warmest month, mean daily high
33°C
Jul and Aug at the habitat CHELSA
Rain a year (median across the range)
580mm
10 months of 25 mm or more in the median year CHELSA
Open-sky light
19–44DLI
Lowest to highest month (DLI) CHELSA
The year in your months, northern hemisphere
  1. Jan
  2. Feb
  3. Mar
  4. Apr
  5. May
  6. Jun
  7. Jul
  8. Aug
  9. Sep
  10. Oct
  11. Nov
  12. Dec
Wet summers: the rain comes April to October, read as a summer growing season. rain rule, CHELSA
Northern hemisphere unless you set your site. The chart is in the habitat's months.

Summary

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.

Quoted from Wikipedia, "Juglans microcarpa", CC BY-SA 4.0.

Cultivation

Seasons

The rain rule reads a summer growing season: 70% of the median year's rain (460 mm of 603 mm) falls in April to October, warmer than the year (wet-season mean 23.9 °C against a yearly mean of 18.9 °C). Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: October to April.

Rain

603 mm in the median year at the habitat, 460 mm of it April to October. Wettest month June at 79 mm, driest month January at 23 mm. Across the grid cells of the range the year's total runs 386 mm to 906 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 580 mm, is the year's rain at the top of the page; the 603 mm here is the median year's, the twelve monthly medians added, which the rain rule reads. Habitat calendar, northern hemisphere; median year across the grid cells of the range, CHELSA.

Light

Open sky over the habitat: 19 to 44 mol/m²/day across the year (daily light integral, median year across the grid cells of the range, CHELSA; the lowest 10th-percentile month across the cells is 17, the highest 90th-percentile month 50).

Warmth and air
Temperature

Coldest: the 1st-percentile night over 44 years at a typical spot in the range is -5.1 °C, the absolute minimum -15.4 °C, 1,137 frost nights in 44 years, 25.8 a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 40.4 °C. Monthly means: the coldest month's mean nightly low 4.8 °C in January (across the grid cells of the range -0.2 °C to 6.5 °C), the warmest month's mean daily high 33.0 °C in August (median year across the grid cells of the range, CHELSA). Cold floor: -5.1 °C, which is the 1st-percentile night over 44 years at a typical spot in the range (NASA POWER).

Humidity

Relative humidity at the habitat: 52 to 55% across the year (monthly means, median year across the grid cells of the range, CHELSA). A figure about the air, saying nothing about how the plant takes water.

How this section is made

Each card states this species' habitat figures with their sources, and what two fixed rules read from them; nothing here says what the plant does, wants or tolerates. The rules · the terms.

Seasons. Read from the median year of CHELSA monthly rainfall and mean temperature across the grid cells of the range: the rain rule takes the smallest set of months carrying 70% of the rain and calls it winter when its mean is more than half a degree below the year's, summer when more than that above, and neither in between; the temperature rule, used only under 120 mm, names the cooler six months when they are at least a degree cooler than the other six. Months are shifted for the other hemisphere only where the temperature curve moves 4 °C or more and the habitat lies 10° or more from the equator. A reading of the curves, not an observation of the plant.

Rain. CHELSA monthly precipitation, median year across the grid cells of the range. The rain that falls where the species is recorded; nothing about how the plant takes water.

Light. CHELSA shortwave radiation at each envelope cell, a daily-mean flux taken to a daily total and converted at 2.07 mol of PAR per MJ. The sky over the habitat, measured; what reaches a plant under a rock, a shrub or a shade cloth is not.

Temperature. NASA POWER daily minima and maxima over 44 years at a typical spot in the range, lapse-corrected -83 m to its elevation; CHELSA monthly means, median year across the grid cells of the range. The cold floor is the 1st-percentile night named in its sentence. Not a measured survival limit for any plant in a pot.

Humidity. CHELSA relative humidity, median year across the grid cells of the range.

Climate across the habitat

Habitat months, northern hemisphere

Habitat climate of Juglans microcarpa through the yearWarmest months July and August, mean daily high 33 °C; coldest month January, mean nightly low 4.8 °C; 603 mm of rain in the median year (the twelve monthly medians added). Medians across the range, from CHELSA; the extremes at the edge from NASA POWER. Habitat months, northern hemisphere.-20°-10°0°10°20°30°40°50°frost40.4° 99th-percentile day, NASA POWER-15.4° lowest night in 44 years, NASA POWER°C · day and nightcold quarter0255075100125mm rainDLI 19–44RH 52–55%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 332 habitat cells, CHELSA cold quarter: the three months around the coldest month's mean nightly low extremes over 44 years at a typical spot in the range, from NASA POWER, marked at the edge, in no month DLI, mol/m²/dayRH %each on its own scale
Figures by month
JanFebMarAprMayJunJulAugSepOctNovDec
Day °C16 / 11–1819 / 14–2122 / 18–2526 / 23–2929 / 27–3232 / 30–3433 / 29–3433 / 28–3530 / 26–3126 / 22–2721 / 16–2216 / 11–18
Night °C5 / 0–77 / 2–810 / 5–1114 / 9–1518 / 14–2021 / 17–2322 / 17–2422 / 17–2419 / 15–2115 / 10–179 / 5–125 / 0–7
Rain mm23 / 14–5428 / 12–5539 / 11–7046 / 17–6875 / 32–10579 / 46–11867 / 44–8960 / 48–8671 / 48–8562 / 34–10829 / 13–7224 / 12–56
DLI21 / 19–2526 / 23–3233 / 29–4040 / 35–4741 / 37–5043 / 41–4944 / 43–4641 / 40–4334 / 33–3828 / 26–3322 / 20–2719 / 17–24
RH %54 / 48–5854 / 46–5852 / 43–5752 / 41–5755 / 43–6055 / 46–6053 / 50–5854 / 51–5655 / 52–5855 / 49–5854 / 47–5854 / 48–58
How this section is made
Each figure is the median across the 332 grid cells holding the 578 in-range records, with the 10th–90th percentile span across those cells after the slash where it differs. A dash is a month one or more of those cells has no figure for in the grid (a variable CHELSA does not carry there), so no median is taken rather than one over fewer cells. Extremes and elevation were read at a typical spot in the range, cell 1191:1603 (30.425, -99.825). Over 44 years there: absolute minimum -15.4 °C, 1st-percentile night -5.1 °C, 99th-percentile day 40.4 °C. Normals: CHELSA V2.1 1981–2010 climatology, 0.05° cells (each the mean of ~36 1 km pixels). Across the range: median and 10th–90th percentile of each month across the 332 distinct grid cells holding 578 of the 578 in-range records; extremes and elevation at the typical cell 1191:1603 (its coldest month's mean nightly low nearest the median across cells); its position is the cell centre. Extremes: NASA POWER (MERRA-2) daily 1981–2024, cell 30.50_-100.000, lapse-corrected -83 m at 6.5 °C/km. Elevation: ETOPO 2022, 573 m (cell mean).

Natural habitat

Native range as published by WCVP; the marker is where the records are densest and decides nothing: the climate was read across the cells of the in-range records placed well enough to read one, not at the marker.
Openly licensed records inside the range, framed on where they fall.
NativeKansas, Oklahoma, New Mexico, Texas, Mexico Northeast · introduced: Tadzhikistan, North Caucasus, Transcaucasus · regions are the level-3 units of the World Geographical Scheme for Recording Plant Distributions, as Kew's World Checklist records ranges, some under historical names such as Yugoslavia or Czechoslovakia (how).
Map marker29.58, -98.631 · in the densest population, 485 records (65% of those in range)
Kew's description“tree” · “temperate” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 743 georeferenced records inside the native range; the climate across the range on the 578 of them placed to within 10 km; the map shows only the 373 openly licensed ones, which alone would put the marker 50 km away. 19 records outside the WCVP native range not used. 165 in-range records are placed to worse than 10 km, or with no stated accuracy (admitted only as a person's observation to three decimals), and stay on the map but off the climate.
How this section is made
The map marker: the openly licensed record nearest the middle of the densest 1° population inside the densest 2° block of the 743 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Juglans microcarpa, photograph 1did not loadJuglans microcarpa, photograph 2did not loadJuglans microcarpa, photograph 3did not loadJuglans microcarpa, photograph 4did not loadJuglans microcarpa, photograph 5did not loadJuglans microcarpa, photograph 6did not load

Photographs: (c) Sam Kieschnick, some rights reserved (CC BY) (2); author not stated, no rights reserved · CC0 (2); (c) Chet Burrier, some rights reserved (CC BY) (2).

Similar habitat climate The 6 nearest by mean daily high, mean nightly low and rain, month by month. How.

Yucca reverchonii Yucca reverchonii San Angelo yucca Photo: CC BY, CK2AZAristolochia coryi Aristolochia coryi Cory's dutchman's pipe Photo: CC BY, Michelle W. （鍾偉瑋）Condalia viridis Condalia viridis Green snakewood Photo: CC BY, Cleveland PowellPanicum hallii Panicum hallii Hall's witchgrass Photo: CC BY, RachelThamnosma texana Thamnosma texana Dutchman's britches Photo: CC BY-SA, Turner BrockmanOenothera calcicola Oenothera calcicola Texas beeblossom Photo: CC BY, Michelle W. （鍾偉瑋）

Other Juglans 14 in the reference

Juglans australis Juglans australis Argentine walnut Photo: CC BY, aacocucciJuglans × bixbyi Juglans × bixbyi Bixby's walnut Photo: CC BY-SA, Douglas GoldmanJuglans californica Juglans californica Southern California black walnut Photo: CC BY, klickloJuglans cinerea Juglans cinerea Butternut Photo: CC BY, treelogicalJuglans hindsii Juglans hindsii Northern California black walnut Photo: CC BY, Irina Mitine Juglans hopeiensis Hebei walnut Juglans jamaicensis Juglans jamaicensis West Indian walnut Photo: CC BY, J. L. Gómez-HechavarríaJuglans major Juglans major Arizona walnut Photo: CC BY, Jo RobertsJuglans mandshurica Juglans mandshurica Manchurian walnut Photo: CC BY, Maria GalkinaJuglans mollis Juglans mollis Mexican walnut Photo: CC BY, Cody HinchliffJuglans neotropica Juglans neotropica Andean walnut Photo: CC BY, GERMAN LEONEL SARMIENTO CRUZJuglans nigra Juglans nigra Black walnut Photo: CC BY, Sandy Wolkenberg all 15 ›

Names & registers

Also known as Juglans rupestris. (GBIF Backbone)

GBIFPOWOIPNIWFOWikidataWikipediaiNaturalist

The record

Family
Juglandaceae
Described by
Berland.
Native to
Kansas, Oklahoma, New Mexico +2
Wild records
743 in range · 373 open

Every figure here is derived from public data by a stated rule and names its source; nothing about this species is written for its page by a person or by AI, apart from the marked, credited quotations. How →

Where this page came from built 2026-10-22
GBIF species record gbif.species answeredasked 2026-10-22GBIF's key 3054372 is Juglans microcarpa Berl.; the page links Kew's Juglans microcarpa Berland., and the name is cited as Kew cites it
GBIF synonyms gbif.synonyms answeredasked 2026-10-22
GBIF common names gbif.vernacular answeredasked 2026-10-22names fetched 2026-10-22
WCVP native range wcvp.distribution answeredas of 2026-06-04
GBIF occurrence records gbif.occurrences answeredas of 2026-10-21GBIF occurrence download https://doi.org/10.15468/dl.hbdw64, of 2026-10-21; 31 records within 1 km of a botanic garden, herbarium or zoo left out (30 at a botanic garden or arboretum, 1 at a herbarium; Wikidata's list)
Habitat climate climate answeredasked 2026-10-22
Daily extremes (NASA POWER) climate.extremes answeredasked 2026-10-22NASA POWER (MERRA-2) daily 1981–2024, cell 30.50_-100.000, lapse-corrected -83 m at 6.5 °C/km
Wikidata wikidata answeredasked 2026-10-22
Wikipedia wikipedia answeredasked 2026-10-22
iNaturalist photographs, wild inat.photos.wild answeredasked 2026-10-22from iNaturalist's open data of 2026-09-27: research-grade observations with an open-licence photograph, the 24 whose photographs iNaturalist received last (the open data holds no votes); filled 2026-10-22
iNaturalist photographs, cultivated inat.photos.cultivated not asked
GBIF media gbif.media answeredasked 2026-10-22
OpenAlex papers openalex not askednot yet asked for this reference; a later fill takes the papers from OpenAlex's snapshot

Every source is recorded as having answered, reported nothing, refused, failed, not been asked, or answered twice where one answer is taken (“not taken: two items answered”), and, for a source asked when this page was built, when: the figures are as the source held them that day; a source read from a file (Kew's World Checklist, a GBIF download) says "as of" the file's day instead; a row carried from an earlier build of the page names that build instead. Only “nothing to report” is ever shown as an absence. Records came from 55 datasets via GBIF.org; each carries its own licence.

Cultifolio

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