Research directed by C. Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service

Information on Risk Assessments
Original risk assessment

Washingtonia filifera (Desert Palm, California Washingtonia Palm, California fan palm, cotton palm)

Answer

1.01

Is the species highly domesticated?

y=-3, n=0

n

1.02

Has the species become naturalized where grown?

y=-1, n=-1

y

1.03

Does the species have weedy races?

y=-1, n=-1

n

2.01

Species suited to tropical or subtropical climate(s) (0-low; 1-intermediate; 2-high) – If island is primarily wet habitat, then substitute “wet tropical” for “tropical or subtropical”

See Append 2

1

2.02

Quality of climate match data (0-low; 1-intermediate; 2-high) see appendix 2

1

2.03

Broad climate suitability (environmental versatility)

y=1, n=0

n

2.04

Native or naturalized in regions with tropical or subtropical climates

y=1, n=0

2.05

Does the species have a history of repeated introductions outside its natural range? y=-2

?=-1, n=0

y

3.01

Naturalized beyond native range y = 1*multiplier (see Append 2), n= question 2.05

y

3.02

Garden/amenity/disturbance weed y = 1*multiplier (see Append 2)

n=0

y

3.03

Agricultural/forestry/horticultural weed y = 2*multiplier (see Append 2)

n=0

n

3.04

Environmental weed y = 2*multiplier (see Append 2)

n=0

3.05

Congeneric weed y = 1*multiplier (see Append 2)

n=0

y

4.01

Produces spines, thorns or burrs

y=1, n=0

y

4.02

Allelopathic

y=1, n=0

4.03

Parasitic

y=1, n=0

n

4.04

Unpalatable to grazing animals

y=1, n=-1

y

4.05

Toxic to animals

y=1, n=0

n

4.06

Host for recognized pests and pathogens

y=1, n=0

n

4.07

Causes allergies or is otherwise toxic to humans

y=1, n=0

n

4.08

Creates a fire hazard in natural ecosystems

y=1, n=0

y

4.09

Is a shade tolerant plant at some stage of its life cycle

y=1, n=0

4.1

Tolerates a wide range of soil conditions (or limestone conditions if not a volcanic island)

y=1, n=0

y

4.11

Climbing or smothering growth habit

y=1, n=0

n

4.12

Forms dense thickets

y=1, n=0

y

5.01

Aquatic

y=5, n=0

n

5.02

Grass

y=1, n=0

n

5.03

Nitrogen fixing woody plant

y=1, n=0

n

5.04

Geophyte (herbaceous with underground storage organs -- bulbs, corms, or tubers)

y=1, n=0

n

6.01

Evidence of substantial reproductive failure in native habitat

y=1, n=0

n

6.02

Produces viable seed.

y=1, n=-1

y

6.03

Hybridizes naturally

y=1, n=-1

y

6.04

Self-compatible or apomictic

y=1, n=-1

y

6.05

Requires specialist pollinators

y=-1, n=0

n

6.06

Reproduction by vegetative fragmentation

y=1, n=-1

n

6.07

Minimum generative time (years) 1 year = 1, 2 or 3 years = 0, 4+ years = -1

See left

19

7.01

Propagules likely to be dispersed unintentionally (plants growing in heavily trafficked areas)

y=1, n=-1

n

7.02

Propagules dispersed intentionally by people

y=1, n=-1

y

7.03

Propagules likely to disperse as a produce contaminant

y=1, n=-1

n

7.04

Propagules adapted to wind dispersal

y=1, n=-1

n

7.05

Propagules water dispersed

y=1, n=-1

n

7.06

Propagules bird dispersed

y=1, n=-1

y

7.07

Propagules dispersed by other animals (externally)

y=1, n=-1

7.08

Propagules survive passage through the gut

y=1, n=-1

y

8.01

Prolific seed production (>1000/m2)

y=1, n=-1

n

8.02

Evidence that a persistent propagule bank is formed (>1 yr)

y=1, n=-1

y

8.03

Well controlled by herbicides

y=-1, n=1

n

8.04

Tolerates, or benefits from, mutilation, cultivation, or fire

y=1, n=-1

y

8.05

Effective natural enemies present locally (e.g. introduced biocontrol agents)

y=-1, n=1

Total score:

11.5

Source

Notes

1.01

No evidence

1.02

(1)naturalized in s. Nevada [contradicted by refence #3, which argues that it is native] (2)It is extensively planted as an ornamental in semiarid and subtropical regions of the world, and has naturalized in some places. [Reference does not distinguish between W. robusta and W. filifera]

(1)http://www.ars-grin.gov/cgi-bin/npgs/html/tax_search.pl?Washingtonia+filifera (2)http://www.fs.fed.us/database/feis/plants/tree/wasfil/distribution_and_occurrence.html (3)http://www.xeri.com/Moapa/relict.htm

1.03

No evidence

2.01

(1)Native Habitat: Springs and streams (often with alkaline pH) on borders of Colorado Desert, California, and in Southwest Arizona where roots have regular access to water. (2)Native range: Northern America: Mexico - Baja Norte; United States - Arizona [s.w.], California [s.e.] [distribution is mainly desert and Mediterranian; very little/no range extentind into tropics and subtropics.] (3)the species originates from the Sacramento River in California

(1)Horticopia A to Z. CD-ROM database. (2)http://www.ars-grin.gov/cgi-bin/npgs/html/tax_search.pl?Washingtonia+filifera (3)http://mobot.mobot.org/cgi-bin/search_vast

2.02

(1)naturalized in s. Nevada (2)It is extensively planted as an ornamental in semiarid and subtropical regions of the world [9], and has naturalized in some places [24].[Reference does not distinguish between W. robusta and W. filifera]

(1)http://www.ars-grin.gov/cgi-bin/npgs/html/tax_search.pl?Washingtonia+filifera (2)http://www.fs.fed.us/database/feis/plants/tree/wasfil/distribution_and_occurrence.html

2.03

(1)Hardiness Range 9A to 11 (2)Climate groups: Arid and Mediterranean. (3)California palm communities separate into three distinct zones: the hydric zone, the oasis-proper, and the oasis-desert ecotone. (4)California palm occurs at elevations below 3,500 feet (1,067 m). [Reference does not distinguish between W. robusta and W. filifera] (5)over-irrigation and rainy weather could initiate root rot; They reportedly suffer and often die from root rot when irrigated. suited for planting in dry urban landscapes. [susceptible to disease in wet environments] (6)Plant community: Creosote Bush Scrub

(1)Horticopia A to Z. CD-ROM database. (2)Horticopia-Plant Master. Cd-ROM database. (3)http://www.fs.fed.us/database/feis/plants/tree/wasfil/distribution_and_occurrence.html (4)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html (5)http://edis.ifas.ufl.edu/ST669 (6)http://www.calflora.org/cgi-bin/calflora_query?one=T&where-calrecnum=8336

2.04

(1)Native Habitat: Springs and streams (often with alkaline pH) on borders of Colorado Desert, California, and in Southwest Arizona where roots have regular access to water. (2)Native range: Northern America: Mexico - Baja Norte; United States - Arizona [s.w.], California [s.e.] [little or no tropical/subropical distribution in nature]

(1)Horticopia A to Z. CD-ROM database. (2)http://www.ars-grin.gov/cgi-bin/npgs/html/tax_search.pl?Washingtonia+filifera

2.05

It is extensively planted as an ornamental in semiarid and subtropical regions of the world [9], and has naturalized in some places [24].

http://www.fs.fed.us/database/feis/plants/tree/wasfil/distribution_and_occurrence.html

3.01

(1)naturalized in s. Nevada [contradicted by refence #3, which argues that it is native] (2)It is extensively planted as an ornamental in semiarid and subtropical regions of the world, and has naturalized in some places. [Reference does not distinguish between W. robusta and W. filifera]

(1)http://www.ars-grin.gov/cgi-bin/npgs/html/tax_search.pl?Washingtonia+filifera (2)http://www.fs.fed.us/database/feis/plants/tree/wasfil/distribution_and_occurrence.html (3)http://www.xeri.com/Moapa/relict.htm

3.02

Germination: So easy that young seedlings can become weeds under mature palms [garden weed]

http://www.floridata.com/ref/w/wash_fil.cfm

3.03

No evidence

3.04

(1) 'On both East and West Maui, these palms are commonly cultivated in urban and residential areas from sea level to 4,000 ft (1,219 m). In hot, lowland, urban areas near water sources, such as wetlands, areas close to the water table, irrigation ditches, and ponds, Washingtonia spp. are extremely prolific and well established. In these areas, numerous seedlings and saplings are observed germinating wherever possible. Seedlings have even been observed to come up through cracks in concrete sidewalks and streets. Plants spread rapidly from cultivation, invade wetland areas, and crowd out native species. At higher, dryer elevations and areas where rainfall amounts are high, Washingtonia spp. do tend to spread, but not nearly as rapidly or as much. Island wide control at this time is probably not feasible due to widespread distribution. Wetland area managers near infestations should be familiar with these palms and try to remove them as early as possible to avoid major infestations.'

(1)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm (2)http://edis.ifas.ufl.edu/ST669 (3)http://www.floridata.com/ref/w/wash_fil.cfm (4)http://wric.ucdavis.edu/wricguestbook00.html

3.05

' In Florida, Washingtonia robusta threatens native plant communities in coastal wetland and beach habitat in southern parts of the state.'

(1)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm (2)

4.01

Trunk has no thorns. Petioles are armed with sharp thorns.

Horticopia A to Z. CD-ROM database.

4.02

(1)California palm fruit allelopathically inhibits germination and growth of other species under laboratory conditions. (2)Abs: 'The germination- and growth-inhibiting activity of water soluble extracts of Washingtonia filifera fruits was investigated. Paper chromatographic separation of the extract revealed the presence of two inhibiting zones of germination and growth. The fast moving -inhibitor was further separated by TLC into four components, one of which appears to be abscisic acid (ABA) and the rest phenolic substances. Gibberellic acid (GA3) was found to neutralize the germination and growth inhibiting ability of the inhibitor -complex. Besides these, a slow moving inhibitory zone of germination and growth was due to the presence of phenolic substances.' (3) Abs: 'Leachates from dry fruits of W. filifera inhibited the germination of wheat, lettuce, red cabbage and cucumber seeds. The inhibitory effect was partly neutralized by kinetin (20 mg/l) and gibberellic acid (50 mg/l). The effect of kinetin wa

(1)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html (2) Khan, M. I. 1998. Allelopathic potential of dry fruits of Washingtonia filifera (L. Linden) H. Wendl III. Inhibitors of germination and growth. Pakistan Journal of Botany. Vol.30, No.2, pp.245-252, 20 ref. (3)Khan, M. I.1982. Khan, M. I.Allelopathic potential of dry fruits of Washingtonia filifera: Inhibition of seed germination. Physiologia Plantarum. Vol.54, No.3, pp.323-328, 19 ref.

4.03

No evidence

4.04

deer reistant

http://www.laspilitas.com/lists/deerfire.htm

4.05

(1)Coyotes, foxes and birds eat the fruit and disseminate the seeds. Seeds germinate readily after they pass through the animals digestive tract. (2)Birds generally consume only the fruit, not the seed [32]. The western and mountain bluebird and the cedar waxwing, however, eat both fruit and seed, disseminating the seed in droppings.

(1)Horticopia A to Z. CD-ROM database. (2)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html

4.06

(1) 'California palm is resistant to most fungal and bacterial infections [26]. A crown rot (Penicillium vermoeseni) sometimes infects trees that have been injured by lightning strikes or fire. Lightning-injured trees may be difficult to detect because palms do not generally show lightning disfigurement [18]. Palms, however, are occasionally decapitated by lightning [39]. California palm is the specific host of the giant palm borer beetle (Dynapate wrightii). Larvae of this insect feed on the wood [26,32] and can weaken or kill trees [8].'
(2) AB: "Guava wilt disease (GWD) (caused by Penicillium vermoensenii ) has resulted in the loss of more than half the guava plantings in the northeastern region of South Africa. Control measures, other than eradication of diseased trees, do not exist. Consequently, it was of critical importance for the guava industry that a cultivar with an adequate degree of tolerance was found, and that trees with such tolerance were rapidly multiplied for commercial release befor

(1) http://www.fs.fed.us/database/feis/plants/tree/wasfil/management_considerations.html
(2) Vos, J. E.; Schoeman, M. H.; Berjak, P.; Watt, M. P.; Toerien, A. J. (2000) ET: In vitro selection and commercial release of Guava Wilt resistant rootstocks. Editors: Fokkema, N. J.; Beek, M. A.; Steekelenburg, N. A. M. van; Samyn, G.; Maas, J. L.; Robinson, T. L.; Verhoyen, M. N. J. Acta Horticulturae, 2000, No.513, pp.69-79, 17 ref.

4.07

' Fruits and seeds of Washingtonia filifera were known to be used as a food resource by the Cahuilla Indians of the southern California deserts. The nutritional analysis of W. filifera fruits was compared with analyses of other Indian and non-Indian food plants. W. filifera fruits have a higher carbohydrate content than other Indian food plants, but significantly less protein. Protein content was less than half that in Prosopis juliflora, a common oasis plant and food resource of the Cahuilla. Results suggest that W. filifera fruits had the potential to be an important dietary mainstay.'

Cornett, J. W. 1987. Nutritional value of desert fan palm fruits. Principes, Vol.31, No.4, pp.159-161, 10 ref.

4.08

(1)The armed petioles of falling leaves may be dangerous (Dehgan 1998). The shaggy thatch of dead leaves that is left on the trunk is a fire hazard (Brickell and Zuk 1997).
(2) 'These dead fronds are known to be a fire hazard

(1)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htmhttp:/
/www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm(2)http://edis.ifas.ufl.edu/ST669

4.09

(1)Exposure Full sun (2)Full sun (3)California palm is moderately shade tolerant when young, becoming intolerant with age [Reference does not distinguish between W. robusta and W. filifera] (4)Not grown in shade or indoors (5)Needs Full Sun (6)The position of this tall and robust fan palm should be sunny

(1)Horticopia A to Z. CD-ROM database. (2)Horticopia-Plant Master. Cd-ROM database. (3)http://www.fs.fed.us/database/feis/plants/tree/wasfil/distribution_and_occurrence.html (4)http://www.premierpalms.com/pages/cotton.htm (5)http://www-horticulture.tamu.edu/aransas/califfanpalm.htm (6)http://www.palmenexpress.de/html/plants.html

4.1

Soil Condition Loamy, sandy, clay, acidic, neutral, alkaline, tolerates salt, drought tolerant

Horticopia A to Z. CD-ROM database.

4.11

A Palm - Arecaceae. Not a vine.

Horticopia A to Z. CD-ROM database.

4.12

(1) 'They are well established in dry, hot coastal wetland areas, produce abundant seeds spread by fruit eating birds, and form dense thickets.' [does not distinguish between W. robusta and W. filifera] (2)Uncommon but locally abundant [implies forming fairly dense stands in native range] (3)California palm forms open to dense groves in moist areas, often providing 100 percent of overstory cover [reference does not distinguish between W. robusta and W. filifera]

(1)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm (2)Hiickman et al. 1990. The Jepson Manual of Higher plants of California. University of California Press (3)http://www.fs.fed.us/database/feis/plants/tree/wasfil/distribution_and_occurrence.html

5.01

Horticopia A to Z. CD-ROM database.

5.02

Palm - Arecaceae

Horticopia A to Z. CD-ROM database.

5.03

Palm - Arecaceae

Horticopia A to Z. CD-ROM database.

5.04

Palm - Arecaceae

Horticopia A to Z. CD-ROM database.

6.01

(1)Natural populations of California palm are reseeding well. (2)The very many flowers, of color flesh, give rise to thousands of round small fruits, of color black shining, the size of peas, containing each one a smooth and brilliant seed of color dark chestnut.

(1)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html (2)http://translate.google.com/translate?hl=en&sl=fr&u=http://www.france-palmier.com/especes-rustiques/washingtonia-filifera.htm&prev=/search%3Fq%3DWashingtonia%2Bfilifera%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DG

6.02

Coyotes, foxes and birds eat the fruit and disseminate the seeds. Seeds germinate readily after they pass through the animals digestive tract.

Horticopia A to Z. CD-ROM database.

6.03

'Latin name: Washingtonia filifera (L. Linden) H. Wendl. and Washingtonia robusta H. Wendl. (Oppenheimer and Bartlett 2002). There are also hybrids between the two, which are sometimes referred to as Washingtonia x filabusta.' 'Washingtonia x filabusta: A hybrid between the two species exists and is commonly grown and sold in the horticulture trade (Dehgan 1998, White Tank Palms 2000). Hybrid trees tend to have characteristics of both species. The species are hard to distinguish when young (Riffle 1998).'

http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm

6.04

(1)Washingtonia are hermaphrodites and only one specimen can produce viable seeds. (2)Pollination is predominantly insect-mediated (J. W. Cornett, in [22]), but self-pollination may also occur

(1)http://translate.google.com/translate?hl=en&sl=fr&u=http://www.france-palmier.com/especes-rustiques/washingtonia-filifera.htm&prev=/search%3Fq%3DWashingtonia%2Bfilifera%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DG (2)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html

6.05

(1)Pollination is predominantly insect-mediated (J. W. Cornett, in [22]), but self-pollination may also occur (2)Pollination: Not known (3) 'It had not previously been known whether the desert fan palm Washingtonia filifera (of which populations in different localities were genetically uniform) was pollinated by wind or by insects. … but the abundance and diversity of species, not only Hymenoptera but also Coleoptera, Diptera and Lepidoptera, suggest that the flowers of the desert palm are pollinated by insects.'

(1)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html (2)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm (3)Cornett, J. W.. 1986. Arthropod visitors at Washingtonia filifera (Wendl) flowers. Pan-Pacific Entomologist.Vol.62, No.3, pp.224-225, 5 ref.

6.06

vegetative reproduction does not occur

http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html

6.07

(1)Cultivated trees have flowered at age 19 [26], but the age at which trees growing under natural conditions first flower is unreported. (2)When supplied optimal conditions, this variety is considered to have a medium growth rate.

(1)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html (2)http://plants.gardenbed.com/73/7254_lan.asp

7.01

Probably not - no evidence that the propagules have any means of attachment.

Horticopia A to Z. CD-ROM database.

7.02

Ornamental palm.

http://www.ars-grin.gov/cgi-bin/npgs/html/tax_search.pl?Washingtonia+filifera

7.03

Probably not, seeds relatively large. (1)Fruit size 3/8" diameter. (2)Fruits are brownish -black, to 6 mm long, 3.5 to 4 mm broad.

(1) Meerow, A. W. 1992. Betrocks Guide to Landscape Palms. Betrocks Informaiton Systems Inc. Cooper City. Florida. (2) Blombery A & Rodd, T. 1982. Palms.Robertson Publishers. Australia.

7.04

No evidence

7.05

No evidence

7.06

(1)Coyotes, foxes and birds eat the fruit and disseminate the seeds. Seeds germinate readily after they pass through the animals digestive tract. (2)Birds generally consume only the fruit, not the seed [32]. The western and mountain bluebird and the cedar waxwing, however, eat both fruit and seed, disseminating the seed in droppings.

(1)Horticopia A to Z. CD-ROM database. (2)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html

7.07

[caching by rats? But no evidence]

7.08

(1)Coyotes, foxes and birds eat the fruit and disseminate the seeds. Seeds germinate readily after they pass through the animals digestive tract. (2)Seeds are disseminated primarily by the coyote [7,40]. Because of its fruit-eating habit and broad range of travel between water sources, coyote often transport seeds over considerable distances. ...A comparison of seed collected from the ground surface and seed collected from coyote scat showed that the pericarp was missing from 94 percent of coyote-consumed seed. Removal of the pericarp increases the probability of germination. Sixty-three percent of coyote-consumed seed tested in this study germinated, as compared to 34 percent of that in the control group [8].

(1)Horticopia A to Z. CD-ROM database. (2)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html

8.01

Probably not, seeds relatively large. (1)A heavy crop for an individual tree probably approaches 10,000 fruits. (2)Fruit size 3/8" diameter. (3)Fruits are brownish -black, to 6 mm long, 3.5 to 4 mm broad. [A large tree can have a canopy > 10 m2; Reference does not distinguish between W. robusta and W. filifera]

(1)http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html (2) Meerow, A. W. 1992. Betrocks Guide to Landscape Palms. Betrocks Informaiton Systems Inc. Cooper City. Florida. (3) Blombery A & Rodd, T. 1982. Palms.Robertson Publishers. Australia.

8.02

Seed remains viable in seedbanks for up to 6 years

http://www.fs.fed.us/database/feis/plants/tree/wasfil/botanical_and_ecological_characteristics.html [Reference does not distinguish between W. robusta and W. filifera]

8.03

Chemical control: Not known.

http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm

8.04

PLANT RESPONSE TO FIRE : Fire releases saplings suppressed by the shade of shrubs. Young palms, freed from competition for water and sunlight, grow vigorously in fire-opened sites [40]. Flower and fruit production nearly doubles in crown-scorched trees during the first postfire growing season [8,32]. ...Fire is an essential element of California palm regneration and oasis maintenance. Fire suppression, practiced in many oases for over 60 years, has resulted in dense understories of brush and young palms. The Thousand Palms Oasis, for example, located in the Colorado Desert, California, developed very little understory for 10 to 15 years following its last fire. Saltgrass was the understory pioneer. It was displaced by a dense growth of mesquite (Prosopis juliflora; P.  pubescens) and goldenbush. After 35 years of fire suppression the oasis supported a dense, tall undergrowth with a humid microclimate. Litter accumulations were "massive" [40]. California palm's ability to resist fire under such highly

http://www.fs.fed.us/database/feis/plants/tree/wasfil/fire_effects.html

8.05

Biological control: Not known.

http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm