Isoetes butleri (limestone quillwort)

Plate 1 figs. a–h · 8 separate observations

Isoetes butleri, photographed by Ryan Sorrells — fig. a Ryan Sorrells, CC BY 4.0 / 2022-05-10 / obs. 196671032

Isoetes butleri, photographed by Sam Kieschnick — fig. f Sam Kieschnick, CC BY 4.0 / obs. 117904546

Isoetes butleri, photographed by Noah Yawn — fig. g Noah Yawn, CC BY 4.0 / obs. 117937540

Isoetes butleri, photographed by Nathan Aaron — fig. h Nathan Aaron, CC BY 4.0 / obs. 65494337

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 10 botanical countries

Native distribution of Isoetes butleri, 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
Arkansas	ARK
Georgia	GEO
Illinois	ILL
Kansas	KAN
Kentucky	KTY
Missouri	MSO
Oklahoma	OKL
Tennessee	TEN
Texas	TEX

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.

Where it actually grows measured, from 82 observations

Condition	5th percentile	Median	95th percentile
Coldest month, mean daily low	-7.9 °C	-0.1 °C	4.0 °C
Warmest month, mean daily high	28.7 °C	31.3 °C	34.6 °C
Annual rainfall	880 mm	1,035 mm	1,409 mm
Rainfall in the driest quarter	153 mm	163 mm	288 mm

It is found where winters bring hard frost. This is not care advice and it is not a forecast. It is a measurement: we sampled the climate at every one of the 82 research-grade observations of Isoetes butleri 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.

Also published as 3 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.

Calamaria butleri (Engelm.) Kuntze
Isoetes butleri f. immaculata (Engelm.) Clute
Isoetes butleri var. immaculata Engelm.

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.
USDA PLANTS Database. common name, checklist symbol ISBU. public domain. 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.