Species
+

Ilex opaca Aiton

American Holly, American holly, Christmas Holly, Ittohissishalokpa

Climate known 59 photographs
Add one to my plants Sow seed

Every figure on this page is derived from public data by a stated rule and says its source; nothing here is written by a person or a model, except the Wikipedia passage, which is quoted and marked as such. How it is made.

Summary

Ilex opaca, the American holly, is a species of holly, native to the eastern and south-central United States, from coastal Massachusetts south to central Florida, and west to southeastern Missouri and eastern Texas.

Text from Wikipedia, “Ilex opaca”, CC BY-SA 4.0, quoted as written. Kept separate from everything derived here.

About the genus · Ilex

Ilex or holly is a genus of over 570 species of flowering plants in the family Aquifoliaceae, and the only living genus in that family. Ilex has the most species of any woody dioecious angiosperm genus. The species are evergreen or deciduous trees, shrubs, and climbers from tropics to temperate zones worldwide. More on Wikipedia ›

The opening of Wikipedia, “Holly”, CC BY-SA 4.0, quoted as written.

Family
Aquifoliaceae
Described by
Aiton
Native to
Illinois, Missouri, Oklahoma +24
Wild records
1942 in range· 342 open

At a glance

Warmest month
30°C
Jul, mean day; nights 21 °C (CHELSA)
Rain
1206mm/yr
12 wet months · peak Jul 117 mm (CHELSA)
Light
13–40DLI
mol/m²/day, winter to summer, open sky (CHELSA shortwave)
In short condensed by rule from the cultivation cards · not written by a person
Rain rule: no season, 70% of the rain takes 8 months (March to September and December in the northern hemisphere). Habitat rain 1206 mm a year, wettest July at 117 mm, driest February at 85 mm (habitat calendar, northern hemisphere). Open sky over the habitat: 13 to 40 mol/m²/day. Cold floor -10.4 °C (1st-percentile habitat night, NASA POWER).
Each sentence is one card's own one-line form, written by the same rule as the card (Its year, Rain, Light, Temperature); the note cannot say what a card does not. Months are given for the northern hemisphere (set your site in Settings to change this), and the habitat's own alongside. The cards · the figures.

Also known as Ageria opaca (Aiton) Raf.; Ilex americana Lam.; Ilex aquifolium Marshall; Ilex aquifolium var. opaca (Aiton) Laurentius; Ilex canadensis Marshall and 13 more.

Cultivation

Its year Rain rule: no season, 70% of the rain takes 8 months (March to September and December in the northern hemisphere).

This species’ habitat figures, and what two fixed rules read from them.

The rain rule reads no season: 70% of the year's rain (847 mm of 1206 mm) takes 8 months, March to September and December. Mean temperature moves 23.2 °C between the warmest and coldest month. Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: September to March and June.

Read from the median year of CHELSA monthly rainfall and mean temperature across the envelope cells: 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 gives a season to reverse. A reading of the curves, not an observation of the plant.

Rain Habitat rain 1206 mm a year, wettest July at 117 mm, driest February at 85 mm (habitat calendar, northern hemisphere).

This species’ habitat figures, with their source.

1206 mm a year at the habitat, 847 mm of it March to September and December. Wettest month July at 117 mm, driest February at 85 mm. Across the envelope cells the year's total runs 1096 mm to 1466 mm (10th to 90th percentile of each cell's own year) (median year across the envelope cells, CHELSA; habitat calendar, northern hemisphere).

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

Light Open sky over the habitat: 13 to 40 mol/m²/day.

This species’ habitat figures, with their source.

Open sky over the habitat: 13 to 40 mol/m²/day across the year (daily light integral, median year across the envelope cells, CHELSA; the lowest 10th-percentile month across the cells is 11, the highest 90th-percentile month 41).

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.

Warmth and air Cold floor -10.4 °C (1st-percentile habitat night, NASA POWER).

This species’ habitat figures, with their source.

Temperature

Coldest: the 1st-percentile night over 44 years at the typical cell is -10.4 °C, the absolute minimum -21.1 °C, about 81 frost nights a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 35.1 °C. Monthly means: coldest night -1.1 °C in January (across the envelope cells -4.9 °C to 5.7 °C), warmest day 29.9 °C in July (median year across the envelope cells, CHELSA). Cold floor: -10.4 °C, which is the 1st-percentile night over 44 years at the typical cell (NASA POWER).

NASA POWER daily minima and maxima 1981–2024 at the typical cell, lapse-corrected to its elevation; CHELSA monthly means, median year across the envelope cells, CHELSA. The cold floor is the figure named in its sentence. Not a measured survival limit for any plant in a pot.

Humidity

Relative humidity at the habitat: 56 to 60% across the year (monthly means, median year across the envelope cells, CHELSA). A figure about the air, saying nothing about how the plant takes water.

CHELSA relative humidity, median year across the envelope cells.

The figures the cards read from are in Climate below, and where they came from in Natural habitat.

Climate across the habitat

Habitat climate through the yearMean day from 7 °C in Jan to 30 °C in Jul; mean night from -1 °C in Jan to 21 °C in Jul. The cold quarter, Dec to Feb, is the three months around the coldest night. 1206 mm of rain a year, most in Jul. The bands show the 10th to 90th percentile across 1390 habitat cells. Over 44 years at the typical cell the absolute minimum was -21.1 °C and the 99th-percentile day 35.1 °C; neither is dated to a month. Beneath: daily light integral and relative humidity through the year, each on its own scale.-30°-20°-10°10°20°30°40°frost35.1° 99th-percentile day (undated)-21.1° lowest night in 44 yrs (undated)°C · day and nightcold quarter050100150200mm rainDLI 13–40RH 56–60 %JanFebMarAprMayJunJulAugSepOctNovDec
day night rain 10th–90th percentile across 1390 habitat cells cold quarter: the three months around the coldest night extremes over 44 years at the typical cell, marked at the edge: undated DLI, mol/m²/dayRH %each on its own scale
Figures by month
JanFebMarAprMayJunJulAugSepOctNovDec
Day °C7 / 3–159 / 4–1713 / 8–2119 / 14–2523 / 20–2928 / 24–3130 / 27–3229 / 26–3225 / 22–3020 / 16–2514 / 11–208 / 5–16
Night °C-1 / -5–6-0 / -4–74 / -0–109 / 5–1414 / 10–1819 / 16–2221 / 18–2421 / 18–2417 / 14–2111 / 8–166 / 3–111 / -2–7
Rain mm89 / 74–12385 / 71–134107 / 90–13697 / 80–121106 / 88–132109 / 96–144117 / 99–154108 / 88–143104 / 87–12794 / 77–11791 / 78–12499 / 80–134
DLI15 / 13–1820 / 19–2327 / 26–3034 / 32–3738 / 36–4040 / 39–4138 / 38–4034 / 34–3729 / 27–3123 / 20–2616 / 14–2013 / 11–16
RH %57 / 56–5957 / 55–5856 / 55–5856 / 54–5858 / 56–6059 / 57–6260 / 57–6360 / 58–6459 / 58–6258 / 57–5958 / 57–5958 / 56–60

Each figure is the median across the 1390 grid cells holding the 1852 in-range records, with the 10th–90th percentile span across those cells after the slash where it differs. Extremes and elevation were read at the typical cell 1015:2071 (39.225, -76.425). Over 44 years there: absolute minimum -21.1 °C, 1st-percentile night -10.4 °C, 99th-percentile day 35.1 °C. Normals: CHELSA V2.1 1981–2010 climatology, 0.05° cells (each the mean of ~36 1 km pixels). Envelope: median and 10th–90th percentile of each month across the 1390 distinct grid cells holding the 1852 in-range records; extremes and elevation at the typical cell 1015:2071 (its coldest month's mean night nearest the median across cells); its position is the cell centre. Extremes: NASA POWER (MERRA-2) daily 1981–2024, cell 39.00_-76.250, lapse-corrected -19 m at 6.5 °C/km. Elevation: ETOPO 2022, 2 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 every in-range record's cell, not at the marker.
Openly licensed records inside the range, framed on where they fall.
NativeIllinois, Missouri, Oklahoma, Connecticut, Indiana, Massachusetts, New Jersey, New York, Ohio, Pennsylvania, Rhode I., West Virginia, Texas, Alabama, Arkansas, Delaware, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, District of Columbia
Kew's description“tree” · “temperate”· quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Map marker38.945, -76.698 · in the densest population, 1395 records (72% of those in range)
Evidence usedThe map marker and the climate envelope rest on all 1942 georeferenced records inside the native range; the map shows only the 342 openly licensed ones, which alone would put the marker 2 km away. 7 records outside the range (gardens, roadsides, misidentifications) ignored. 90 in-range records are placed to worse than 10 km and stay on the map but off the climate.
The map markerthe map marker: the openly licensed record nearest the middle of the densest 1° population inside the densest 4° block of the 1942 in-range records; it decides nothing.

Photographs

Ilex opacaIlex opacaIlex opacaIlex opacaIlex opacaIlex opacaIlex opacaIlex opaca

Photographs: no rights reserved · CC0 (8).

Photographs: iNaturalist did not answer when this page was built; what is shown came from the sources that did.

Papers naming this species

Works whose title or abstract names Ilex opaca, most cited first, from OpenAlex (CC0). A mention, not a cultivation source: nothing on this page is drawn from them.

Co‐occurrence based assessment of habitat generalists and specialists: a new approach for the measurement of niche width
Jason D. Fridley, David B. Vandermast, Dane Mitchell Kuppinger, Michael Manthey (2007) · Journal of Ecology
Stand dynamics over 18 years in a southern mixed hardwood forest, Texas, USA
P. A. Harcombe, Christopher Jason Bill, Mark R. Fulton, Jeff S. Glitzenstein (2002) · Journal of Ecology
Interactions for Pollination among Coflowering Shrubs
Beverly J. Rathcke (1988) · Ecology
Hurricanes and the Urban Forest: I. Effects on Southeastern United States Coastal Plain Tree Species
Mary L. Duryea, Eliana Kampf, Ramon C. Littell (2007) · Arboriculture & Urban Forestry
A comparative study of leaf thickness among southern Appalachian hardwoods
Stanley B. Carpenter, Naomi D. Smith (1981) · Canadian Journal of Botany
Contagious seed dispersal beneath heterospecific fruiting trees and its consequences
Charles Kwit, Douglas J. Levey, Cathryn H. Greenberg (2004) · Oikos
Leafminers, Early Leaf Abscission, and Parasitoids: A Tritrophic Interaction
Desmond M. Kahn, Howard V. Cornell (1989) · Ecology
Fruit Production in Mature and Recently Regenerated Forests of the Appalachians
Cathryn H. Greenberg, Douglas J. Levey, David L. Loftis (2007) · Journal of Wildlife Management
Maturation and Germination of Seeds of Ilex opaca
Sumner Albert Ives (1923) · Botanical Gazette

Similar habitat climate the 6 species whose habitat climate is nearest this one's: mean day and night, month by month, and rain on a log scale, in calendar order, so a habitat with the same seasons six months out is far, not near. Nothing else counts: not range, not family.

Other Ilex 9 in the reference

History & registers

Where this page came from built 2026-09-20 · dossier v2 · node
gbif.species answeredcarried from build of 2026-09-19 (offline re-derivation; the backbone was not asked)
gbif.synonyms answeredcarried from build of 2026-09-19 (offline re-derivation; the backbone was not asked)
gbif.vernacular answeredcarried from build of 2026-09-19 (offline re-derivation; the backbone was not asked)
wcvp.distribution answered
gbif.occurrences answeredGBIF occurrence download https://doi.org/10.15468/dl.3h4zam
climate answered
wikidata answeredcarried from build of 2026-09-19 (rederive); that build: carried from build of 2026-09-19 (rederive)
wikipedia answeredcarried from build of 2026-09-19; this build: skipped
inat.taxon not asked
inat.photos.wild answeredcarried from build of 2026-09-19; this build: skipped
inat.photos.cultivated nothing to reportcarried from build of 2026-09-19 (rederive); that build: carried from build of 2026-09-19 (rederive)
commons nothing to reportcarried from build of 2026-09-19 (rederive); that build: carried from build of 2026-09-19 (rederive)
gbif.media answered
openalex answeredcarried from build of 2026-09-19; this build: skipped

Every upstream is recorded as having answered, reported nothing, or refused. Only “nothing to report” is ever shown as an absence. Records came from 59 datasets via GBIF.org; each carries its own licence.