When does MacCart's swallow-wort bloom in Texas?

Most often in April. Across 234 dated, research-grade observations of Metastelma palmeri in Texas, the flowering season runs roughly April to October.

Peak April In flower 234 Examined 258 State Texas

Flowering 234 in flower of 258 examined

100%

96%

94%

100%

96%

81%

43%

Proportion of examined Metastelma palmeri in Texas in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	0	too few examined
Feb	0	0	too few examined
Mar	3	4	too few examined
Apr	33	33	100%	90% to 100%
May	47	49	96%	86% to 99%
Jun	43	45	96%	85% to 99%
Jul	17	18	94%	74% to 99%
Aug	11	11	100%	74% to 100%
Sep	51	53	96%	87% to 99%
Oct	22	27	81%	63% to 92%
Nov	6	14	43%	21% to 67%
Dec	1	4	too few examined

Peak flowering in Apr. Each bar is the share of Metastelma palmeri in Texas 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. 234 of 258 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 4 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 Texas found Metastelma palmeri in flower, not a forecast. It is computed only from observations made in Texas, 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

Metastelma palmeri

MacCart's swallow-wort

Sourcesevery claim on this page

GBIF (iNaturalist Research-grade Observations). Dated flowering annotations in Texas. 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.