Water Howellia (Howellia aquatilis) Surveys in Northern Idaho, 2013 to 2018

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Abstract:

Water howellia (Howellia aquatilis) is an annual aquatic macrophyte that is listed as threatened
by the US Fish and Wildlife Service (USFWS). Globally, it has a disjunct distribution across the
Pacific Northwest. The only known occurrences in Idaho are on floodplains in the Palouse and
Spokane river drainages, in small ponds formed by fluvial processes. Most of this habitat is in
private ownership, which has limited past survey work. This report describes our surveys
conducted in floodplain habitats in northern Idaho:
- Coeur d’Alene River Wildlife Management Area (WMA) on 18 Jul 2013
- St. Maries WMA on 7 Aug 2013
- Brickel Creek west of Spirit Lake on 24-25 Jun 2014
- Hangman Creek near De Smet on 16 Jun 2015
- several creeks and meadows near Deary and Helmer on 10-11 and 19 Jul and 22 Aug 2017
- Pend Oreille WMA on 6 Jul 2018
Surveys were conducted on foot by experienced field botanists at a time when water howellia
was known to be in flower. We used hand-held GPS units to record our routes, all of the ponds
found, and water howellia locations. Woody vegetation proved a useful indicator of latestanding water on the floodplain. We found water howellia only along Hangman Creek, within or
near known occurrences 5 and 6. We considered three ponds within Pend Oreille WMA as
possibly suitable habitat based on the presence of indicator species, primarily water parsnip
(Sium suave) and the floating liverwort Ricciocarpos natans. Elsewhere, ponds were not
considered suitable based on the absence of indicator species. We recommend survey work in
additional river drainages, future monitoring of known sites, and subsequent experimental
introduction via seed to ponds containing habitat indicator species. During our surveys, we
made incidental records for two other rare plants: broadfruit mariposa (Calochortus nitidus) at
Hangman Creek, and arrowleaf sweet coltsfoot (Petasites frigidus var. sagittatus) on Pend
Oreille WMA.

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Shelf Note: Electronic Files - BOTONY: Multiple Species: U21LIC01IDUS

Lichthardt, J., and K. M. Pekas. 2021. Water howellia (Howellia aquatilis) surveys in northern
Idaho, 2013 to 2018. Idaho Natural Heritage Program, Idaho Department of Fish and Game,
Boise, ID. 19 pp. plus appendices