When does onyxflower bloom in California?

Most often in March. Across 553 dated, research-grade observations of Achyronychia cooperi in California, the flowering season runs roughly January to December.

Peak March In flower 553 Examined 568 State California

Flowering 553 in flower of 568 examined

93%

99%

97%

88%

95%

98%

Proportion of examined Achyronychia cooperi in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	76	82	93%	85% to 97%
Feb	135	137	99%	95% to 100%
Mar	201	203	99%	96% to 100%
Apr	38	39	97%	87% to 100%
May	4	4	too few examined
Jun	2	2	too few examined
Jul	0	0	too few examined
Aug	0	0	too few examined
Sep	0	0	too few examined
Oct	7	8	88%	53% to 98%
Nov	40	42	95%	84% to 99%
Dec	50	51	98%	90% to 100%

Peak flowering in Mar. Each bar is the share of Achyronychia cooperi in California observations in which someone actually recorded the reproductive state and found the plant in flower, not the raw number of flowering records. That distinction matters: people observe plants far more in spring than in winter, so a bare count of flowering records partly measures when people go outside. Dividing by the number examined removes that. 553 of 568 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 5 months have fewer than 5 examined observations, so no proportion is drawn for them. This is still a global aggregate and not a forecast for your garden: the same species flowers on different dates in different hemispheres. Where a species has fewer than 30 flowering records we do not draw this chart at all. Computed from 10.15468/dl.wt38fd.

What this is, and what it is not

This is a record of when people in California found Achyronychia cooperi in flower, not a forecast. It is computed only from observations made in California, so it is not the species’ global average dragged onto a map: the same plant flowers on different dates in different places, and that is the entire point of the page.

It will not tell you what your particular plant will do this year. Bloom time moves with the season, with altitude, and with the weather, and a warm February pulls everything forward. We publish the distribution and the sample size, and we refuse to draw a month that too few people examined.

The plant

Achyronychia cooperi

onyxflower

Sourcesevery claim on this page

GBIF (iNaturalist Research-grade Observations). Dated flowering annotations in California. Every record achieved iNaturalist quality grade Research, which is applied upstream at export. 10.15468/dl.wt38fd. Retrieved 2026-07-14.
World Flora Online Plant List. The accepted name. CC0. Retrieved 2026-07-12.