Bacopa caroliniana (blue waterhyssop)

Plate 1 figs. a–h · 8 separate observations

Bacopa caroliniana, photographed by Tom Field — fig. a Tom Field, CC BY 4.0 / 2021-11-08 / obs. 169045606

Bacopa caroliniana, photographed by Neli Kanonerova — fig. b Neli Kanonerova, CC BY 4.0 / obs. 166127396

Bacopa caroliniana, photographed by Kim — fig. c Kim, CC BY 4.0 / obs. 149490319

Bacopa caroliniana, photographed by Jay Horn — fig. d Jay Horn, CC BY 4.0 / obs. 133002999

Bacopa caroliniana, photographed by Lauren McLaurin — fig. e Lauren McLaurin, CC BY 4.0 / obs. 96052125

Bacopa caroliniana, photographed by Eric Knight — fig. f Eric Knight, CC BY 4.0 / obs. 87734693

Bacopa caroliniana, photographed by Austin Smith — fig. g Austin Smith, CC BY 4.0 / obs. 67229277

Bacopa caroliniana, photographed by Adam Pitcher — fig. h Adam Pitcher, CC0 1.0 / obs. 64290444

Every figure is a research-grade observation under CC0, CC BY or CC BY-SA, rehosted with the photographer’s name, the licence and the observation it came from. Photographs under a NonCommercial licence are excluded from this site and are never stored, which costs us a great many pictures and is not negotiable.

Native range 11 botanical countries

Native distribution of Bacopa caroliniana, after Kew’s World Checklist of Vascular Plants. Introduced, extinct and doubtful records are excluded, so this is where the plant is from, not everywhere it now grows.

Region	TDWG code	Continent
Alabama	ALA	NORTHERN AMERICA
Florida	FLA
Georgia	GEO
Louisiana	LOU
Mississippi	MSI
North Carolina	NCA
South Carolina	SCA
Tennessee	TEN
Texas	TEX
Virginia	VRG
Cuba	CUB	SOUTHERN AMERICA

Region boundaries approximated from Natural Earth (public domain) and mapped to TDWG World Geographical Scheme for Recording Plant Distributions (WGSRPD) level-3 botanical countries (Brummitt 2001). Indicative, not the official WGSRPD geometry.

Flowering 81 in flower of 104 examined

33%

100%

90%

100%

93%

82%

57%

Proportion of examined Bacopa caroliniana in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	1	3	too few examined
Feb	1	3	too few examined
Mar	2	6	33%	10% to 70%
Apr	2	4	too few examined
May	7	7	100%	65% to 100%
Jun	9	10	90%	60% to 98%
Jul	11	11	100%	74% to 100%
Aug	27	29	93%	78% to 98%
Sep	14	17	82%	59% to 94%
Oct	4	7	57%	25% to 84%
Nov	3	4	too few examined
Dec	0	3	too few examined

Peak flowering in May. Each bar is the share of Bacopa caroliniana 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. 81 of 104 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.cgje2x.

Where it actually grows measured, from 1,143 observations

Condition	5th percentile	Median	95th percentile
Coldest month, mean daily low	4.6 °C	11.9 °C	16.7 °C
Warmest month, mean daily high	29.9 °C	31.6 °C	33.3 °C
Annual rainfall	1,272 mm	1,438 mm	1,709 mm
Rainfall in the driest quarter	133 mm	188 mm	349 mm

It is barely found anywhere that freezes. This is not care advice and it is not a forecast. It is a measurement: we sampled the climate at every one of the 1,143 research-grade observations of Bacopa caroliniana that carry a coordinate, and this is the range those places actually span. The 5th and 95th percentiles are used rather than the minimum and maximum, because a single cultivated specimen in a heated conservatory should not widen a tropical plant's range to the Arctic.

This is not a hardiness zone. A USDA zone is the average annual extreme minimum temperature. The figure above is the mean daily minimum of the coldest month, which is a different quantity and is typically far warmer. Reading one as the other would place a plant several zones too warm, so we do not publish a hardiness zone, because we do not have one. Climate from CHELSA V2.1 (Karger et al. 2017); occurrences from 10.15468/dl.cgje2x.

Also published as 14 synonyms

A synonym is not an error. It is a record of botanists disagreeing, in print, about where this plant belongs. Each of these was somebody’s considered answer.

Bacopa amplexicaulis (Michx.) Wettst.
Herpestis amplexicaulis (Michx.) Pursh
Herpestis caroliniana Britton, Sterns & Poggenb.
Hydrotrida caroliniana (Walter) Small
Hydrotrida crenulata (Small) Small
Macuillamia amplexicaulis (Michx.) Raf.
Moniera amplexicaulis Michx.
Moniera caroliniana Kuntze
Moniera crenulata Small
Monniera amplexicaulis Michx.
Monniera crenulata Small
Obolaria caroliniana Walter
Septilia caroliniana (Walter) Small
Septilia crenulata (Small) Small

Sourcesevery claim on this page

World Flora Online Plant List. accepted name, authority, classification. CC0. Retrieved 2026-07-12.
iNaturalist. photographs and flowering annotations, CC0 / CC BY / CC BY-SA only. per photograph. Retrieved 2026-06-27.
Wikidata. common name (P1843), joined on the World Flora Online identifier (P7715). CC0. Retrieved 2026-07-13.
Kew, World Checklist of Vascular Plants (WCVP v16). native distribution by TDWG level-3 botanical country, and life form. CC BY 3.0. Retrieved 2026-06-04.

We publish what we can source and we say so when we cannot. This page has no care advice and no toxicity claim, because we do not yet have those from a source we can cite.