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Macrolearia semidentata; photograph Peter de Lange, CC0, iNaturalist via GBIF CC0Peter de Lange, CC0, iNaturalist via GBIF

Macrolearia semidentata (Decne.) Saldivia

Chatham Island Aster; Swamp Aster; Chatham Aster

Asteraceae · Chatham Is.

Cited as Kew's World Checklist cites it, Macrolearia semidentata (Decne.) Saldivia: GBIF's backbone key for this page carries the name with another author, (Decne. ex Hook.) Saldivia.

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Macrolearia semidentata, photograph Peter de Lange, CC0, iNaturalist via GBIFMacrolearia semidentata, photograph Peter de Lange, CC0, iNaturalist via GBIFMacrolearia semidentata, photograph Peter de Lange, CC0, iNaturalist via GBIFMacrolearia semidentata, photograph Tim Park, CC BY, iNaturalist via GBIFMacrolearia semidentata, photograph Peter de Lange, CC0, iNaturalist via GBIFMacrolearia semidentata, photograph Peter de Lange, CC0, iNaturalist via GBIF 24 photographs ›
Habitat figuresfrom few records
Coldest month, mean nightly low
8.6°C
Aug at the habitat, not a floor; extremes not used (sea cell) CHELSA
Warmest month, mean daily high
16°C
Feb at the habitat CHELSA
Rain a year (median across the range)
972mm
12 months of 25 mm or more in the median year CHELSA
Open-sky light
8–43DLI
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.

From few records: 6 records in 6 grid cells. The records.

Cultivation

Seasons

The rain rule reads no short rainy season: 70% of the median year's rain (709 mm of 974 mm) takes 8 months, February to September. Mean temperature moves 5.4 °C between the warmest and coldest month. Months are the habitat's, southern hemisphere; shifted six months for a northern-hemisphere collection: August to March.

Rain

974 mm in the median year at the habitat, 709 mm of it February to September. Wettest month June at 118 mm, driest month January at 61 mm. Across the grid cells of the range the year's total runs 928 mm to 1,131 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 972 mm, is the year's rain at the top of the page; the 974 mm here is the median year's, the twelve monthly medians added, which the rain rule reads. Habitat calendar, southern hemisphere; median year across the grid cells of the range, CHELSA.

Light

Open sky over the habitat: 8 to 43 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 7, the highest 90th-percentile month 43).

Warmth and air
Temperature

Monthly means: the coldest month's mean nightly low 8.6 °C in August (across the grid cells of the range 7.7 °C to 8.8 °C), the warmest month's mean daily high 15.6 °C in February (median year across the grid cells of the range, CHELSA). Cold floor: none read. The nearest figure is 8.6 °C, the coldest month's mean nightly low, August, in the median year (CHELSA); a month's mean of its nightly lows is warmer than the nights a floor is read from. The daily extremes were read at a weather cell that is mostly sea and are not used.

Humidity

Relative humidity at the habitat: 62 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. CHELSA monthly means, median year across the grid cells of the range. No cold floor is read without a daily extremes series; the coldest month's mean nightly low named in its sentence is not one. 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

From few records: this habitat climate is read from 6 records in 6 grid cells; a page says so under 12 records or 5 cells, and shows the figures as read.

Habitat months, southern hemisphere

Habitat climate of Macrolearia semidentata through the yearWarmest month February, mean daily high 16 °C; coldest month August, mean nightly low 8.6 °C; 974 mm of rain in the median year (the twelve monthly medians added). Medians across the range, from CHELSA. Habitat months, southern hemisphere.5°10°15°20°°C · day and nightcold quarter0255075100125150mm rainDLI 8–43RH 62–66%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 6 habitat cells, CHELSA cold quarter: the three months around the coldest month's mean nightly low DLI, mol/m²/dayRH %each on its own scale
Figures by month
JanFebMarAprMayJunJulAugSepOctNovDec
Day °C15 / 15–1516 / 15–1615 / 14–1514 / 13–1413 / 12–1311 / 10–1110 / 9–1110 / 9–1011 / 10–1111 / 10–1112 / 11–1214 / 13–14
Night °C14 / 13–1414 / 13–1414 / 13–1412 / 11–1211 / 10–119 / 8–109 / 8–99 / 8–99 / 8–910 / 9–1011 / 10–1112 / 12–12
Rain mm61 / 57–7270 / 68–8287 / 82–10280 / 76–9494 / 90–111118 / 115–13992 / 87–10590 / 86–10378 / 75–8869 / 66–8067 / 64–7768 / 66–80
DLI42 / 41–4235 / 34–3526 / 25–2617 / 16–1710 / 10–118 / 7–89 / 9–915 / 14–1523 / 22–2331 / 30–3140 / 39–4043 / 42–43
RH %65 / 64–6765 / 64–6764 / 63–6763 / 62–6662 / 62–6562 / 61–6562 / 61–6563 / 62–6663 / 63–6665 / 64–6764 / 63–6766 / 65–68

The daily extremes were read at a NASA POWER cell that is 20% land: neither it nor the next candidates whose coldest month's mean nightly low is within 2 °C of the median across cells sit in a POWER cell that is mostly land, and the rule reads a cold floor only from a cell that is mostly land, so none is read for this species. Nor is the coldest month's mean nightly low taken as one: it is a mean of a month's lows, not its coldest night. What that cell gave over 44 years: absolute minimum 3.6 °C, 1st-percentile night 5.9 °C, 99th-percentile day 18.1 °C.

How this section is made
Each figure is the median across the 6 grid cells holding the 6 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 2676:63 (-43.825, -176.825). 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 6 distinct grid cells holding 6 of the 6 in-range records; extremes and elevation at the typical cell 2676:63 (its coldest month's mean nightly low nearest the median across cells, though its NASA POWER cell is only 20% land and none of the 5 next candidates within 2 °C of the median was mostly land); its position is the cell centre. Extremes: NASA POWER (MERRA-2) daily 1981–2024, cell -44.00_-176.875, lapse-corrected +44 m at 6.5 °C/km. Elevation: ETOPO 2022, 54 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.
NativeChatham Is. · 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 marker-44.029, -176.429 · in the densest population, 49 records (100% of those in range)
Kew's description“temperate” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 49 georeferenced records inside the native range; the climate across the range on the 6 of them placed to within 10 km; the map shows only the 37 openly licensed ones, which alone would put the marker 3 km away. 36 records outside the WCVP native range not used. Under a dozen records behind the climate. 43 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 49 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Macrolearia semidentata, photograph 1did not loadMacrolearia semidentata, photograph 2did not loadMacrolearia semidentata, photograph 3did not loadMacrolearia semidentata, photograph 4did not loadMacrolearia semidentata, photograph 5did not loadMacrolearia semidentata, photograph 6did not load

Photographs: Peter de Lange, CC0, iNaturalist via GBIF (5); Tim Park, CC BY, iNaturalist via GBIF.

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

Pseudopanax chathamicus Pseudopanax chathamicus Chatham Islands Lancewood Photo: CC0, author not statedAstelia chathamica Astelia chathamica Chatham Island Kakaha Photo: CC0, author not statedAustroderia turbaria Austroderia turbaria Chatham Island toe-toe Photo: CC0, author not statedDracophyllum arboreum Dracophyllum arboreum Chatham Island Grass Tree Photo: CC0, author not statedLeptecophylla robusta Leptecophylla robusta Ericaceae Photo: CC0, author not statedMelicytus chathamicus Melicytus chathamicus Chatham Island Māhoe Photo: CC BY, Liadan Dickie

Other Macrolearia 3 in the reference

Macrolearia angustifolia Macrolearia angustifolia Asteraceae Photo: CC BY, Pieter PelserMacrolearia chathamica Macrolearia chathamica Asteraceae Photo: CC0, Peter de LangeMacrolearia colensoi Macrolearia colensoi Leatherwood Photo: CC BY, Oscar Dove

Names & registers

Also known as Aster semidentatus; Eurybia semidentata; Olearia semidentata. (GBIF Backbone)

GBIFPOWOIPNIWikidata

The record

Family
Asteraceae
Described by
(Decne.) Saldivia
Native to
Chatham Is.
Wild records
49 in range · 37 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 12221737 is Macrolearia semidentata (Decne. ex Hook.) Saldivia; the page links Kew's Macrolearia semidentata (Decne.) Saldivia, 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
Habitat climate climate answeredasked 2026-10-22
Daily extremes (NASA POWER) climate.extremes answeredasked 2026-10-22NASA POWER (MERRA-2) daily 1981–2024, cell -44.00_-176.875, lapse-corrected +44 m at 6.5 °C/km; read, and set aside: NASA POWER's cell is mostly sea (20% land), so no cold floor is shown
Wikidata wikidata answeredasked 2026-10-22
Wikipedia wikipedia nothing to reportasked 2026-10-22
iNaturalist taxon inat.taxon not asked
iNaturalist photographs, wild inat.photos.wild not asked
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 8 datasets via GBIF.org; each carries its own licence.

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