Exacum affine Balf.f. ex Regel
German-violet; Persian-violet; Tiddly-winks
Cited as Kew's World Checklist cites it, Exacum affine Balf.f. ex Regel: GBIF's backbone key for this page carries the name with another author, Balf.fil.
29 photographs › At a glance
- Jan
- Feb
- Mar
- Apr
- May, shaded
- Jun, under 5 mm of rain
- Jul, under 5 mm of rain
- Aug, under 5 mm of rain
- Sep
- Oct, shaded
- Nov, shaded
- Dec, shaded
Summary
Exacum affine, known commercially as the Persian violet, is a species of plant in the family Gentianaceae. It is endemic to Socotra, part of Yemen, though its popularity and cultivation around the world have made it an occasional greenhouse weed. Its natural habitat is rocky areas. This is a small herbaceous biennial plant with dark green, ovate leaves. More on Wikipedia ›
Quoted from Wikipedia, "Exacum affine", CC BY-SA 4.0.
Cultivation
Seasons
The rain rule reads a rainy season with no name: 70% of the median year's rain (168 mm of 215 mm) falls in May and October to December, whose mean temperature, 25.4 °C, is within half a degree of the year's, 25.2 °C, so it is neither the cooler nor the warmer part of the year. Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: April to June and November.
Rain
215 mm in the median year at the habitat, 168 mm of it May and October to December. Wettest month December at 65 mm, driest month August at 1 mm; 3 months under 5 mm. Across the grid cells of the range the year's total runs 136 mm to 270 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 227 mm, is the year's rain at the top of the page; the 215 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: 32 to 46 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 31, the highest 90th-percentile month 47).
Warmth and air
Coldest: the 1st-percentile night over 44 years at a typical spot in the range is 12.9 °C, the absolute minimum 9.8 °C, no frost in 44 years (NASA POWER daily minima). Warmest: the 99th-percentile day is 40.2 °C. Monthly means: the coldest month's mean nightly low 20.1 °C in January (across the grid cells of the range 17.1 °C to 22.1 °C), the warmest month's mean daily high 31.0 °C in May (median year across the grid cells of the range, CHELSA). Cold floor: 12.9 °C, which is the 1st-percentile night over 44 years at a typical spot in the range (NASA POWER).
Relative humidity at the habitat: 59 to 66% 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 -277 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
Mean daily high from 25 °C in Jan to 31 °C in May; mean nightly low from 20 °C in Jan and Feb to 26 °C in May and Jun. The cold quarter, Dec to Feb, is the three months around the coldest month's mean nightly low, centred on the 2 months in a row that tie for it. 215 mm of rain in the median year (the twelve monthly medians added), the wettest month Dec. The bands show the 10th to 90th percentile across 21 habitat cells. Over 44 years at a typical spot in the range (NASA POWER) the absolute minimum was 9.8 °C and the 99th-percentile day 40.2 °C; neither is dated to a month. Beneath: daily light integral and relative humidity through the year, each on its own scale.
Figures by month
| Figure | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Day °C | 25 / 23–26 | 26 / 24–27 | 28 / 27–30 | 30 / 29–31 | 31 / 29–32 | 29 / 28–30 | 28 / 26–29 | 28 / 25–28 | 28 / 26–29 | 28 / 27–29 | 27 / 25–28 | 26 / 24–26 |
| Night °C | 20 / 17–22 | 20 / 17–22 | 22 / 19–23 | 24 / 21–26 | 26 / 23–27 | 26 / 24–27 | 24 / 23–25 | 24 / 22–25 | 24 / 22–25 | 23 / 20–24 | 22 / 19–24 | 21 / 18–23 |
| Rain mm | 11 / 4–16 | 6 / 3–8 | 5 / 4–8 | 9 / 7–12 | 21 / 15–33 | 4 / 3–10 | 2 / 1–28 | 1 / 1–26 | 9 / 4–21 | 36 / 7–46 | 46 / 3–59 | 65 / 6–80 |
| DLI | 34 / 32–36 | 39 / 38–41 | 44 / 44–46 | 46 / 46–47 | 42 / 41–45 | 37 / 36–38 | 36 / 36–37 | 36 / 36–37 | 38 / 37–38 | 39 / 38–40 | 36 / 34–37 | 32 / 31–34 |
| RH % | 60 / 56–66 | 60 / 58–63 | 59 / 57–63 | 60 / 58–62 | 63 / 59–67 | 62 / 59–68 | 62 / 58–70 | 62 / 59–71 | 66 / 61–72 | 63 / 61–66 | 62 / 57–65 | 61 / 55–66 |
How this section is made
Natural habitat
How this section is made
Photographs
Photographs: (c) Павлик Лисицын, some rights reserved (CC BY) (4); (c) Morten Ross, some rights reserved (CC BY) (2).
Related
Similar habitat climate The 6 nearest by mean daily high, mean nightly low and rain, month by month. How.
Jatropha unicostata Sibru Photo: CC BY, Arabella Willing
Withania riebeckii Solanaceae Photo: CC BY, Morten Ross
Euphorbia schimperi Euphorbiaceae Photo: CC BY, Morten Ross
Euphorbia spiralis Euphorbiaceae Photo: CC BY, Morten Ross Boswellia aspleniifolia Burseraceae 
Cyanixia socotrana Iridaceae Photo: CC BY, Morten RossOther Exacum 1 in the reference
Names & registers
Also known as Exacum gracilipes. (GBIF Backbone)
The record
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 answeredasked 2026-10-22GBIF's key 5829210 is Exacum affine Balf.fil.; the page links Kew's Exacum affine Balf.f. ex Regel, and the name is cited as Kew cites itgbif.synonyms answeredasked 2026-10-22gbif.vernacular answeredasked 2026-10-22names fetched 2026-10-22wcvp.distribution answeredas of 2026-06-04gbif.occurrences answeredasked 2026-10-22GBIF occurrence download https://doi.org/10.15468/dl.hbdw64, of 2026-10-21; 44 records of GBIF's key 8307593, Exacum affine Balf.f. ex Regel (Kew's file holds it as Exacum affine Balf.f. ex Regel (accepted)): GBIF occurrence search API; 10 records within 1 km of a botanic garden, herbarium or zoo left out (5 at a botanic garden or arboretum, 5 at a herbarium; Wikidata's list)climate answeredasked 2026-10-22climate.extremes answeredasked 2026-10-22NASA POWER (MERRA-2) daily 1981–2024, cell 17.00_53.750, lapse-corrected -277 m at 6.5 °C/kmwikidata answeredasked 2026-10-22wikipedia answeredasked 2026-10-22inat.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 2026-10-22inat.photos.cultivated not askedgbif.media answeredasked 2026-10-22none of the photographs on this page is credited to GBIF: those shown are other sources', and GBIF's were the same photographs or were set aside by the photograph rulesopenalex not askednot yet asked for this reference; a later fill takes the papers from OpenAlex's snapshotEvery 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 21 datasets via GBIF.org; each carries its own licence.