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Iris giganticaerulea; photograph (c) Lauren McLaurin, some rights reserved (CC BY) CC BY(c) Lauren McLaurin, some rights reserved (CC BY) · observed growing wild · 2026-03-28

Iris giganticaerulea Small

Giant blue iris

Iridaceae · Alabama, Louisiana +1 · listed by its genus as a bulb, tuber or caudex

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Iris giganticaerulea, photograph (c) Lauren McLaurin, some rights reserved (CC BY)Iris giganticaerulea, photograph author not stated, no rights reservedIris giganticaerulea, photograph (c) Brandon Johnson, some rights reserved (CC BY)Iris giganticaerulea, photograph (c) Daniel McClosky, some rights reserved (CC BY)Iris giganticaerulea, photograph (c) GobyHunter, some rights reserved (CC BY)Iris giganticaerulea, photograph (c) Wendy McCrady, some rights reserved (CC BY) 44 photographs ›
Habitat figures
Cold floor (1 night in 100)
-4.0°C
Record low -12.8 °C in 44 years, at a typical spot in the range NASA POWER
Warmest month, mean daily high
31°C
Jun, Jul and Aug at the habitat CHELSA
Rain a year (median across the range)
1,730mm
12 months of 25 mm or more in the median year CHELSA
Open-sky light
18–40DLI
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
Rain spread: 70% of the median year's rain takes 8 months, so no short rainy season. rain rule, CHELSA
Northern hemisphere unless you set your site. The chart is in the habitat's months.

Summary

Iris giganticaerulea, the giant blue iris, or Louisiana Iris, is a species of iris, in the subgenus Limniris, in the series Hexagonae. It is a rhizomatous perennial, from northern America. It has long bright green leaves, very tall stems and one or two musky fragrant flowers in a range of blue shades (pale, bright, dark, lavender and violet) or rarely white.

Quoted from Wikipedia, "Iris giganticaerulea", CC BY-SA 4.0.

Cultivation

Grouped as a bulb, tuber or caudex, listed under the genus Iris in the archetype table, and Kew describes it as “rhizomatous geophyte”.

Seasons

The rain rule reads no short rainy season: 70% of the median year's rain (1,268 mm of 1,763 mm) takes 8 months, December to March and June to September. Mean temperature moves 16.4 °C between the warmest and coldest month. Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: December to March and June to September.

Rain

1,763 mm in the median year at the habitat, 1,268 mm of it December to March and June to September. Wettest month June at 194 mm, driest month November at 120 mm. Across the grid cells of the range the year's total runs 1,455 mm to 1,931 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 1,730 mm, is the year's rain at the top of the page; the 1,763 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: 18 to 40 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 16, the highest 90th-percentile month 41).

Warmth and air
Temperature

Coldest: the 1st-percentile night over 44 years at a typical spot in the range is -4.0 °C, the absolute minimum -12.8 °C, 754 frost nights in 44 years, 17.1 a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 38.4 °C. Monthly means: the coldest month's mean nightly low 8.0 °C in January (across the grid cells of the range 4.7 °C to 9.3 °C), the warmest month's mean daily high 31.3 °C in July (median year across the grid cells of the range, CHELSA). Cold floor: -4.0 °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: 59 to 63% 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 -16 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.

Group. Listed under the genus Iris in the archetype table, and Kew describes it as “rhizomatous geophyte”. A group is taken only where Kew's description of the species agrees with the table's listing. The table gives no figure and no prose; the cold floor is the habitat's alone.

Climate across the habitat

Habitat months, northern hemisphere

Habitat climate of Iris giganticaerulea through the yearWarmest months June, July and August, mean daily high 31 °C; coldest month January, mean nightly low 8.0 °C; 1,763 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°frost38.4° 99th-percentile day, NASA POWER-12.8° lowest night in 44 years, NASA POWER°C · day and nightcold quarter050100150200250mm rainDLI 18–40RH 59–63%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 28 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 / 14–1718 / 16–1821 / 20–2224 / 24–2528 / 28–2931 / 30–3231 / 31–3331 / 31–3329 / 29–3025 / 25–2621 / 20–2217 / 15–18
Night °C8 / 5–910 / 6–1113 / 10–1416 / 14–1721 / 19–2224 / 22–2425 / 24–2625 / 24–2523 / 21–2418 / 15–1913 / 10–159 / 6–11
Rain mm140 / 124–155144 / 116–158134 / 104–155121 / 104–132133 / 109–146194 / 134–229190 / 113–216171 / 86–202148 / 94–175121 / 98–137120 / 111–136147 / 127–160
DLI19 / 17–1924 / 22–2431 / 29–3137 / 36–3840 / 39–4139 / 38–4038 / 37–4036 / 35–3732 / 31–3327 / 26–2821 / 19–2218 / 16–18
RH %60 / 58–6160 / 58–6060 / 57–6060 / 57–6061 / 59–6162 / 60–6363 / 60–6463 / 58–6461 / 57–6259 / 57–5959 / 57–5960 / 58–60
How this section is made
Each figure is the median across the 28 grid cells holding the 28 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 1192:1801 (30.375, -89.925). Over 44 years there: absolute minimum -12.8 °C, 1st-percentile night -4.0 °C, 99th-percentile day 38.4 °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 28 distinct grid cells holding 28 of the 28 in-range records; extremes and elevation at the typical cell 1192:1801 (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_-90.000, lapse-corrected -16 m at 6.5 °C/km. Elevation: ETOPO 2022, 8 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.
NativeAlabama, Louisiana, Mississippi · 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 marker30.297, -90.153 · in the densest population, 208 records (80% of those in range)
Kew's description“rhizomatous geophyte” · “subtropical” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 261 georeferenced records inside the native range; the climate across the range on the 28 of them placed to within 10 km; the map shows only the 80 openly licensed ones, which alone would put the marker 27 km away. 22 records outside the WCVP native range not used. 233 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 of the 261 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Iris giganticaerulea, photograph 1did not loadIris giganticaerulea, photograph 2did not loadIris giganticaerulea, photograph 3did not loadIris giganticaerulea, photograph 4did not loadIris giganticaerulea, photograph 5did not loadIris giganticaerulea, photograph 6did not load

Photographs: (c) Lauren McLaurin, some rights reserved (CC BY); author not stated, no rights reserved · CC0; (c) Brandon Johnson, some rights reserved (CC BY); (c) Daniel McClosky, some rights reserved (CC BY); (c) GobyHunter, some rights reserved (CC BY); (c) Wendy McCrady, some rights reserved (CC BY).

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

Clinopodium coccineum Clinopodium coccineum Scarlet calamint Photo: CC0, author not statedChrysoma pauciflosculosa Chrysoma pauciflosculosa Woody goldenrod Photo: CC0, author not statedLilaeopsis carolinensis Lilaeopsis carolinensis Carolina grasswort Photo: CC BY, Scott Allen DavisLobelia floridana Lobelia floridana Florida lobelia Photo: CC0, author not statedRhynchospora latifolia Rhynchospora latifolia Giant Whitetop Photo: CC0, author not statedSymphyotrichum adnatum Symphyotrichum adnatum Scale-leaf aster Photo: CC0, author not stated

Other Iris 182 in the reference

Iris acutiloba Iris acutiloba Iridaceae Photo: CC0, author not stated Iris aitchisonii Iridaceae Iris alberti Iris alberti Iridaceae Photo: CC BY, Islam Galymzhanov Iris albomarginata Iridaceae Iris alexeenkoi Iris alexeenkoi Iridaceae Photo: CC BY, info.botdb.ruIris aphylla Iris aphylla Stool iris Photo: CC BY, Мирослав СоболевIris arenaria Iris arenaria Iridaceae Photo: CC BY, Oleksii VasyliukIris atropurpurea Iris atropurpurea Coastal Iris Photo: CC BY, Nachman bonesIris aucheri Iris aucheri Aucher-Eloy Iris Photo: CC BY-SA, Anas A. Emad Iris baldshuanica Iridaceae Iris barbatula Iris barbatula Iridaceae Photo: CC BY, Morten RossIris barnumiae Iris barnumiae Iridaceae Photo: CC BY-SA, Mehrad Rousta all 183 ›

Names & registers

Also known as Iris aurilinea; Iris citricristata; Iris elephantina; Iris fluviatilis; Iris giganticaerulea f. miraculosa and 6 more. (GBIF Backbone)

GBIFPOWOIPNIWFOWikidataWikipediaiNaturalist

The record

Family
Iridaceae
Described by
Small
Native to
Alabama, Louisiana, Mississippi
Wild records
261 in range · 80 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 2026-10-22
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; 5 records within 1 km of a botanic garden, herbarium or zoo left out (5 at a botanic garden or arboretum; 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_-90.000, lapse-corrected -16 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 9 datasets via GBIF.org; each carries its own licence.

Cultifolio

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