CPC Plant Profile: Water Howellia
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Plant Profile

Water Howellia (Howellia aquatilis)

Howellia aquatilis's tiny, above-water flowers. Photo Credit: Ed Guerrant
Description
  • Global Rank: G3 - Vulnerable
  • Legal Status: Federally Threatened
  • Family: Campanulaceae
  • State: CA, ID, MT, OR, WA
  • Nature Serve ID: 136199
  • Date Inducted in National Collection: 04/04/1991

How can any plant found in California, Washington, Idaho and Montana, especially one with over 150 known occurrences, possibly qualify as Threatened under the Endangered Species Act Howellia aquatilis is such a plant, and it richly deserves protection. Over two thirds of the known sites are restricted to just one of only six clusters of populations, and the entire species occupies a total area of less than 200 acres of a very particular, ecologically fine-tuned, and easily disrupted habitat. It was discovered in 1897 by brothers Thomas and Joseph Howell on Sauvie Island, which is near Portland, Oregon, a state in which it has since become extinct. This aquatic annual species is distinctive enough that it is the only member of its genus. In its short life, plants produce two kinds of flowers. Early flowers remain underwater and never open. Even so, they consistently produce seeds, which are necessarily the result of self-pollination. Flowers produced later do emerge above the surface of the water and open into what look like tiny white lobelias. The above-water flowers, which are also primarily self-pollinating, do have the potential to accept pollen from other plants. Due to the predominance of inbreeding, Howellia has an extremely uniform genetic makeup throughout its entire range. In addition to limited genetic diversity, the species' very particular environmental requirements may also limits it long term future prospects. Although this plant is aquatic, its seeds do not germinate under water. Since seeds germinate in the fall and overwinter as seedlings (another curious property), Howellia requires a dry autumn followed by a wet spring in order to establish for the year. In addition to seasonally fluctuating ponds, Howellia requires fertile, highly organic soils, which are generally maintained by deciduous trees surrounding the ponds. Therefore, disturbances to the surrounding forest community also impact this threatened species. Research indicates that Howellia does not form a persistent seed bank, making this annual especially dependant on year to year reproductive success in order to persist.

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Updates
  • 09/16/2020
  • Reintroduction

Transplant experiments were preformed to determine the viability of transplanting seedlings into ponds that still contain water (H. aquatilis will not germinate in anaerobic environments). Two years after the plantings, plants were still present at the two transplantation sites. However, one of the sites experienced an 85% decrease in population side between the first and second year of monitoring. Additionally, while the sites contained reproductive plants after the first year, no new plants were apparent after the second year. The possibility of further decline, followed by local extinction, is high for both ponds.

  • 09/16/2020
  • Propagation Research

Germination trials preformed on MT populations by Lesica (1992) found that seeds had significantly lower germination rates after 8 months of dried storage. Additionally, plants grown from older seeds had reduced vigor (Lesica 1992). However, different monitoring studies indicated that seeds retained germinability for at least 2 years (Schassberger and Shelly 1991, Shelly 1992). These conflicting germination results may reflect variability in duration of seed viability, perhaps correlated with the extent of wetland drying in a year (Shelly 1992 based on work done by Lesica 1991, USFWS 1996)

Nature Serve Biotics
  • 05/02/2017

Historically, this species occurred over a large area of the Pacific Northwest, but extant populations are mostly clustered in 2 main population centers, one in eastern Washington and one in northwestern Montana. The species has also been found recently at several sites in Mendocino County, California. Extirpated in Oregon. Genetic variability is low throughout its range; the species may represent a single genotype that is narrowly adapted to specific habitat conditions. Populations vary widely in size from year to year and very wet or very dry seasons can have a detrimental effect on abundance. The large fluctuations in annual numbers and low genetic variability indicates that isolated populations may be vulnerable to extirpation. Populations near the larger ""population centers"" may be inherently more resilient.

Edward Guerrant, Ph.D.
  • 01/01/2010

Drainage of aquatic habitat for urban and agricultural development (Meinke 1982) Invasion of noxious weeds: e.g. reed canary grass (Phalaris arundinacea), and purple loosestrife (Lythrum salicaria. (WNHP 1999, USFWS 1994)). Invasion of reed canary gr

Edward Guerrant, Ph.D.
  • 01/01/2010

Most sites containing H. aquatilis are < 1 acre (FWS web page) As of 2000 (Rush and Gamon 2000, USFWS 1996, CDFG 2001): The main geographical areas where H. aquatilis is found include: 1-- ID (Latah Co.) 1 occurrence 3 --WA (Spokane, Clark and Pierce Co) 45 occurrences in Spokane Co., 5 occurrences in Pierce Co. and One (1) in Clark County. 1 - MT (Lake and Missoula Co.) A total of 101 occurrences in Lake and Missoula Counties. 1 - CA (Medocino Co, rediscovered in 1996). 6 occurrences.

Edward Guerrant, Ph.D.
  • 01/01/2010

Germination trials preformed on MT populations by Lesica (1992) found that seeds had significantly lower germination rates after 8 months of dried storage. Additionally, plants grown from older seeds had reduced vigor (Lesica 1992). However, different monitoring studies indicated that seeds retained germinability for at least 2 years (Schassberger and Shelly 1991, Shelly 1992). These conflicting germination results may reflect variability in duration of seed viability, perhaps correlated with the extent of wetland drying in a year (Shelly 1992 based on work done by Lesica 1991, USFWS 1996). Germination trials and observations. Howellia aquatilis has relatively large seeds, and is capable of germinating in both the dark and at low temperatures, which are characteristic of plants that generally do not form persistent seed banks (Lesica 1990). H. aquatilis germination was 2-3 times greater under an above-freezing, fluctuating temperature regime, possibly the consequence of a mechanism that prevents germination of seeds that are buried too deep (Lesica 1990). While H. aquatilis requires submersion to grow and reproduce, it cannot germinate under anaerobic conditions (Lesica 1990). The seed bank peaks in September, immediately after seed dispersal. By mid-October, approximately 25 percent of the seed bank has germinated, and the seed bank is reduced to 40% of the September peak. Disease and predation reduce the seeds back to 10 percent of the September peak by mid-May (Lesica 1990). Optimal development for H. aquatilis occurs in ponds that dry down in wet years but do not dry up too early in dry year (Lesica 1990, 1992). Relatively shallow organic and mineral sediments with high levels of nutrient availability provide optimal H. aquatilis habitat. Disturbances that cause a decrease in pond fertility will have strongly adverse effects on H. aquatilis populations (Lesica 1990). Germination trials in a variety of soils indicate that H. aquatilis has difficulty completing its lifecycle in non-organic substrates (Lesica 1992). Water pH and water conductivity are often highly related, and are probably important in determining the distribution of H. aquatilis, but not the abundance in an area (Lesica 1990). Howellia aquatilis is negatively associated with dissolved solids, indicating that this species is probably restricted to fresh water (Lesica 1992). Abundant graminoid cover may exclude H. aquatilis from some ponds (Lesica 1992). Individuals/population can vary dramatically annually. Monitoring showed that in 1985 and 1987, 10,000 plants established, but in 1986 there were fewer than 100 plants (Lesica et al. 1988). Transplant experiments were preformed to determine the viability of transplanting seedlings into ponds that still contain water (H. aquatilis will not germinate in anaerobic environments). Two years after the plantings, plants were still present at the two transplantation sites. However, one of the sites experienced an 85% decrease in population side between the first and second year of monitoring. Additionally, while the sites contained reproductive plants after the first year, no new plants were apparent after the second year. The possibility of further decline, followed by local extinction, is high for both ponds. If the populations persist, these results would suggest that limited dispersal events keep H. aquatilis from establishing in suitable ponds. If they do not persist, it is possible that transplanted ponds were unsuitable for H. aquatilis over the longer term (Roe and Shelly 1991). Protein electrophoresis was used to examine the genetic structure of 4 populations. 8 enzymes on 18 loci were encoded. All the loci were monomorphic for the same allele, both within and between populations. H. aquatilis appears to have only one homozygous genotype throughout its entire range It is likely that these populations have not had enough time since separation to diverge genetically. It is difficult to determine if these plants are rare because they are genetically impoverished or vice versa (Lesica et al. 1988).

Edward Guerrant, Ph.D.
  • 01/01/2010

Listed as Threatened under the Endangered Species Act. Critical habitat was not designated, because the Fish and Wildlife Service was concerned about the publication of site-specific maps of critical habitat (USFWS 1994).

Edward Guerrant, Ph.D.
  • 01/01/2010

Continue inventory studies (WNHP 1999) Continue population and transect monitoring (Shelly 1992). Research seed bank dynamics further. Seed bank production is likely to be higher in years when the pond retains more water, but subsequent effects of high water level on seed bank persistence is unknown (Shelly 1992). Research the longevity of seed viability, especially in regards to wetness/dryness of the environment (USFWS 1996, Rush and Gamon 2000). Detailed study of population dynamics in relation to pond drying and other climatic influences (Shelly 1992, Rush and Gamon 2000). Also, population dynamics in relation to snowpack depth, annual precipitation and temperature patterns (USFWS 1996). Further study the effect of predation and disease on seed bank and population (Shelly 1992) Study the successional pathways and rates of emergent freshwater ponds. Determine if artificial habitat maintenance can be used to maintain populations (USFWS 1996). Study the degree of threat posed by reed canary grass (Phalaris arundinacea) (Rush and Gamon 2000). Investigate the relationship between nutrient availability and the abundance of Howellia (Shelly 1992). Maintain a forested buffer with a minimum width of 300ft around aquatic habitats. Logging and vegetation disturbing activities in this buffer should be minimized, but activities may be necessary to maintain the buffer (management for mountain pine beetle kill, prescribed burning) (Shelly 1992). The potential effects of prescribed burning should be examined prior to burning areas with H. aquatilis. Early season burns likely do not have an adverse effect, because the ponds still contain water (USFWS 1996). Create and maintain corridors between ponds for animal movement to facilitate seed dispersal and maintain metapopulation dynamics (Shelly 1992). Determine the mechanisms by which seeds are dispersed between ponds (Rush and Gamon 2000) Check suitable but currently unoccupied ponds to determine if species is colonizing new sites (USFWS 1996). Preservation of sites that have a broad scope of ponds at different stages of succession, providing suitable colonization habitats as ponds that currently contain H. aquatilis become inappropriate (Lesica 1988). Restore populations in areas where the plant was know to occur historically (Lesica 1988). Model rates of colonization and extirpation (Rush and Gamon 2000).

Edward Guerrant, Ph.D.
  • 01/01/2010

Seeds cannot be saved using conventional means (i.e.. Drying and freezing.) Determine successful means of maintaining viable seed or plant material. Collect and store seeds or plant material.

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Photos
Nomenclature
Taxon Howellia aquatilis
Authority Gray
Family Campanulaceae
CPC Number 2278
ITIS 34580
USDA HOAQ
Common Names howellia | water howellia
Associated Scientific Names Howellia aquatilis
Distribution CA, ID, OR (extirpated), MT, WA.CA: Mendocino County ID: Latah Co.OR: formerly Willamette ValleyWA: Puget trough, Columbia BasinMT: Swan River Drainage
State Rank
State State Rank
California S2
Idaho S1
Montana S3
Oregon S1
Washington S2S3
Habitat

Restricted to small pothole ponds or orphaned river oxbows that are generally less than 3 ft (1 m) deep, but occasionally up to 6 ft (2 m) deep. Ponds are typically in a matrix of dense forest vegetation, and are nearly always surrounded by broadleaf deciduous trees. Bottoms of wetlands contain clay and organic sediments. Habitats are filled by snowmelt run-off and spring rains, and then dry out to varying degrees by the end of the growing season (Shelly 1992). Found in elevations between 3m (10 ft) in WA to 1350 m (4420 ft) in MT (Shelly 1992). Almost always bordered with one of the following broadleaf trees: Popullus trichcarpa, P. tremuloides, Fraxinus latifolia. Most wetlands have a well-developed shrub component composed of plants such as Cornus stolonifera, and Spirea douglasii (USFWS 1996)

Ecological Relationships

Howellia aquatilis produces two types of flowers: submerged cleistogamous flowers and emergent chasmogamous flowers. Cleistogamous flowers are characteristically self-pollinating; chasmogamous flowers are predominantly self-pollinating, but can be cross-pollinated. (Lesica et al. 1988) At least in Montana, submerged flowers appear in early May, shortly after the dormant seedlings have begun to grow, and emergent flowers bloom when stems reach the surface, from late June until August. Seed dispersal from underwater fruits begins in early June and extends into late summer as emergent fruits ripen. The two different flowers extend seed production over most of growing season (Lesica 1990 in Shelly 1992), but it appears as though cleistogamous flowers produce the majority of seeds (Lesica 1988). This species only grows in zones within wetlands that are seasonally inundated yet dry out in late summer or early fall. This annual inundation may help keep competing vegetation from becoming too well established (WNHP, 1999). Seed germination occurs in the fall in dried, aerobic portions of the pond and plants then over-winter as dormant seedlings (Lesica 1990 in Shelly 1992). Since seeds do not germinate without exposure to the high oxygen levels, the population levels in a particular year are directly influenced by the extent to which the pond dries out at the end of the previous growing season (Shelly 1992). Seeds produced by submergent flowers likely sink immediately. While seeds from emergent flowers may float a short distance, they do not float for long and there is likely not long distance dispersal within ponds. Broken stems with fruits have been observed floating in water, providing some longer distance dispersal within the same wetland, but the species is mostly restricted to quiet water (Shelly and Moseley 1988 in Shelly 1992). It is possible that waterfowl and mammal (deer, bear, moose) ingestion distributes seeds between ponds (Shelly 1992), but this phenomenon has not been investigated.Fire may have historically influenced H. aquatilis distribution. Intense fire late in the growing season has the potential to extirpate a population. With this fire regime, clusters of small populations would be would be less likely to be eliminated than one large population. Fire early in the growing season may offset organic mat build-up in ponds, benefiting the population. The primary effect of fire would be to remove trees, influencing the drying regime of the ponds (Shelly 1992).In Montana, the restriction of H. aquatilis clusters of populations in closely adjacent ponds suggests metapopulation dynamics. Metapopulation dynamics may be critical for the survival of species that inhabit a shifting mosaic of habitats. It may also help the population persist in the midst of environmental stochastity, since multiple populations can serve as a source of colonists (USFWS 1996).In Montana, the pothole ponds inhabited appear to be at an early succession stage. Aquatic grasses, sedges, pondweeds, and burreeds characterize these ponds. With increasing sedimentation and accumulation of organic matter, and the lowering of the water table, these habitats eventually develop into sedge meadows, and H. aquatilis is not present. In ponds that are more successionally advanced, and remain wet for the majority of the growing season, Typha latifolia is frequent. H. aquatilis occurs with T. latifolia, but these ponds support less vigorous populations of H. aquatilis (Shelly 1988).

Pollinators
Common Name Name in Text Association Type Source InteractionID
Other
Self Only Not Specified Link
Self Only Not Specified Link
Reintroduction
Lead Institution State Reintroduction Type Year of First Outplanting

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