Lophophora williamsii (Lem. ex Salm-Dyck) J.M.Coult.

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

The rain rule reads a summer growing season: 70% of the year's rain (252 mm of 359 mm) falls in May to September, warmer than the year (wet-season mean 23.3 °C against a yearly mean of 19.6 °C). Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: November to March.

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.

This species’ habitat figures, with their source.

359 mm a year at the habitat, 252 mm of it May to September. Wettest month July at 61 mm, driest March at 8 mm. Across the envelope cells the year's total runs 300 mm to 506 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.

This species’ habitat figures, with their source.

Open sky over the habitat: 27 to 47 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 23, the highest 90th-percentile month 50).

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.

This species’ habitat figures, with their source.

Coldest: the 1st-percentile night over 44 years at the typical cell is -0.1 °C, the absolute minimum -6.8 °C, about 4 frost nights a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 36.5 °C. Monthly means: coldest night 6.9 °C in January (across the envelope cells 4.9 °C to 9.1 °C), warmest day 30.4 °C in May (median year across the envelope cells, CHELSA). Cold floor: -0.1 °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.

Relative humidity at the habitat: 47 to 58% 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.