Melocactus zehntneri (Britton & Rose) Luetzelb.

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

The rain rule reads a sharp season: 70% of the year's rain (443 mm of 590 mm) falls in January to May. The temperature curve is flat, 3.5 °C between the warmest and coldest month, so the growing-season rule does not infer a growing season from it. Months are the habitat's, southern hemisphere, within 10° of the equator; with no thermal season there there is no season to reverse, so they are not shifted for a collection elsewhere.

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.

590 mm a year at the habitat, 443 mm of it January to May. Wettest month March at 139 mm, driest September at 6 mm. Across the envelope cells the year's total runs 498 mm to 919 mm (10th to 90th percentile of each cell's own year) (median year across the envelope cells, CHELSA; habitat calendar, southern 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: 28 to 44 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 25, the highest 90th-percentile month 45).

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 16.1 °C, the absolute minimum 14.2 °C, no frost in 44 years (NASA POWER daily minima). Warmest: the 99th-percentile day is 39.2 °C. Monthly means: coldest night 19.2 °C in August (across the envelope cells 16.4 °C to 21.1 °C), warmest day 32.5 °C in October (median year across the envelope cells, CHELSA). Cold floor: 16.1 °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: 54 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.