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 robusta (Mexican fan palm; not synonymous with W. filifera -- e.g. see http://rimmo.mur.csu.edu.au/~plants/Sorting/Washingtonia.html)

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

2

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

2.04

Native or naturalized in regions with tropical or subtropical climates

y=1, n=0

y

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

y

3.05

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

n=0

4.01

Produces spines, thorns or burrs

y=1, n=0

y

4.02

Allelopathic

y=1, n=0

n

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

y

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

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

8.03

Well controlled by herbicides

y=-1, n=1

y

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:

15

Source

Notes

1.01

No evidence

1.02

(1)naturalized in s. California & Florida (2) 'In Hawai'i, Washingtonia filifera, W. robusta, and a hybrid W. x filabusta are commonly cultivated and naturalized on the island of Maui.' 'They are spreading in Florida, Hawai'i, and Australia.' 'In Florida, Washingtonia robusta threatens native plant communities in coastal wetland and beach habitat in southern parts of the state.'

(1)http://www.ars-grin.gov/cgi-bin/npgs/html/tax_search.pl?Washingtonia+robusta (2)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm

1.03

No evidence

2.01

(1)Native habitat: Mexico. (2) 'This palm is native to the desert mountain valleys and canyons of Sonora and Baja Mexico.'

(1)Horticopia A-Z . CD-ROM database. (2)http://www.floridata.com/ref/w/wash_rob.cfm

2.02

It is a popular landscape plant in Florida, California and Arizona and in areas where it is hardy throughout the world.'

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

2.03

(1)Hardiness range: 9A - 11. (2) 'Hardiness:
USDA Zone 9a (-3.9° C to -6.6° C)
USDA Zone 9b (-1.2° C to -3.8° C)
USDA Zone 10a (1.6° C to -1.1° C)
USDA Zone 10b (4.4° C to 1.7° C)
USDA Zone 11 (above 4.5° C) (3)They grow very well in semi-arid climates but have also proved to be highly adaptable, growing well in coastal districts, mountainous regions and from the tropics to cool-temperate climates. (4)The palms grow in semi-arid, desert regions, usually forming colonies near water in gorges or canyons.(5) Both species of Washingtonia dislike wet, humid conditions. [some conflicting information -- may be restricted to dry climates?] 

(1)Horticopia A-Z . CD-ROM database. (2)http://plantsdatabase.com/go/51656/ (3)Jones, D.L. 1995. Palms Throughout the World. Smithsonian Institution Press, Washington, DC (4)http://arboretum.arizona.edu/palms.htm (5)http://www.rosedownmill.freeserve.co.uk/waro.html

2.04

(1)Native habitat: Mexico. (2) 'This palm is native to the desert mountain valleys and canyons of Sonora and Baja Mexico.'

(1)Horticopia A-Z . CD-ROM database. (2)http://www.floridata.com/ref/w/wash_rob.cfm

2.05

(1)'It is a popular landscape plant in Florida, California and Arizona and in areas where it is hardy throughout the world.' (2) ' Even with protection, they are only 'half-hardy' in the UK climate.'

(1)http://www.floridata.com/ref/w/wash_rob.cfm (2)http://www.plantapalm.com/vpe/photos/rosedownmill/washingtonia_robusta-rdm.htm

3.01

(1)naturalized in s. California & Florida (2) 'In Hawai'i, Washingtonia filifera, W. robusta, and a hybrid W. x filabusta are commonly cultivated and naturalized on the island of Maui.' 'They are spreading in Florida, Hawai'i, and Australia.' 'In Florida, Washingtonia robusta threatens native plant communities in coastal wetland and beach habitat in southern parts of the state.'

(1)http://www.ars-grin.gov/cgi-bin/npgs/html/tax_search.pl?Washingtonia+robusta (2)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm

3.02

(1) 'Concern is expressed about the increased planting of Washingtonia robusta in S. Florida. The palm appears attractive when young but it grows rapidly, has a skirt of dead leaves in the first few years, becomes nude with age, when the slender stem, ultimately too tall for a hurricane area, looks like a telegraph pole with a small tuft of leaves at the summit; it has also become a weed. Seeds germinate readily in any nook, at the side of steps, in containers and in hedges, and plants can disrupt masonry and threaten roof overhangs. ...' [garden/amenity weed]

(1)Morton, J. F. 1989. The Mexican Washington Palm is not an asset in Florida landscaping. Proceedings of the Florida State Horticultural Society, 1989, Vol.102, pp.101-106, 45 ref.

3.03

No evidence

3.04

'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/WG209

3.05

(1) 'In Death Valley National Monument, part of the Mojave and Colorado Desert Biosphere Reserve, Washingtonia filifera is considered a minor pest that needs localized control (Loope 1992).' (2)on the contrary, evidence indicates that it is a native species in the Mohave, and the it's charactarization by some people as a newly evolved invasive weed were misguided.

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

4.01

(1)Trunk has no thorns (2) 'These (leaves) are glossy rich green and grow to about 5' long and 4' wide and are borne on 3' orange stems that are edged with vicious saw-tooth spines.'

(1)Horticopia A-Z . CD-ROM database. (2)http://www.floridata.com/ref/w/wash_rob.cfm

4.02

No evidence

4.03

No evidence

4.04

fronds not eaten by deer

http://monroe.ifas.ufl.edu/key_deer_plants.htm

4.05

No evidence

4.06

(1)List of 23 fungi associated with W. robusta. (2)The responses of 20 species of ornamental palms and one cycad (Cycas revoluta ) to two populations of Rotylenchulus reniformis , from southern Florida were studied in two greenhouse experiments... Sections from Washingtonia robusta roots infected by R. reniformis females showed the nematode feeding on syncytia formed by endodermal, pericyclic, and vascular parenchyma cells in a manner similar to that reported for other monocot hosts of the reniform nematode. (3)R. reniformis is one of the most widely distributed species and is of major global economic importance to agriculture. The reniform nematode has been found to be the most important nematode pest of papaya. It is generally serious where the previous crop grown was pineapple. (4) Abs: 'A previously undescribed bud rot of 5-yr-old W. robusta trees in Fla., caused by P. palmivora, is described. Symptoms included wilt, eventual desiccation of the youngest leaves to a straw brown color, and tan-colored necro

(1)http://nt.ars-grin.gov/fungaldatabases/all/FindRecOneFungusFrame.cfm (2) Inserra, R. N.; Dunn, R. A.; Vovlas, N. 1994. Host response of ornamental palms to Rotylenchulus reniformis. Journal of Nematology, Vol.26, No.4 Supp., pp.737-743, 10 ref. (3)http://www.extento.hawaii.edu/Kbase/crop/Type/rotyl_pap.htm (4)Atilano, R. A. 1982. Phytophthora bud rot of Washingtonia palm. Atilano, R. A. Plant Disease. Vol.66, No.6, pp.517-519, 13 ref. (5)http://www.botany.unimelb.edu.au/botanyunimelb/1pages/
research/labs/mycology/duriansite/phytophthora.html

4.07

No evidence

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) 'As the leaves die, they fall against the trunk to create the "hula skirt" effect for which this palm is famous. Unfortunately this shaggy skirt of leaves is a fire hazard and provides a home for rats and other undesirable creatures.'

(1)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm (2)http://www.floridata.com/ref/w/wash_rob.cfm

4.09

(1)Partial shade or partial sun to full sun. 'Mexican Washington Palm needs full sun for best growth but grows well in partial shade.' (2) 'Light: It does best in bright sunny conditions but Washington palm will tolerate some shade.'

(1)Horticopia A-Z . CD-ROM database. (2)http://www.floridata.com/ref/w/wash_rob.cfm

4.1

(1)Soil: Soil Condition Loamy, sandy, clay, acidic, neutral, alkaline, tolerates salt well, drought tolerant, tolerates wetness (2)It will tolerate poor soil

(1)Horticopia A-Z . CD-ROM database. (2)http://palms.ifas.ufl.edu/PDFs/Palm%20Fact%20Sheets/Washington%20palm.pdf

4.11

Not a vine - a palm.

Horticopia A-Z . CD-ROM database.

4.12

'They are well established in dry, hot coastal wetland areas, produce abundant seeds spread by fruit eating birds, and form dense thickets.'

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

5.01

Terrestrial

Horticopia A-Z . CD-ROM database.

5.02

An evergreen palm

Horticopia A-Z . CD-ROM database.

5.03

An evergreen palm - Arecaceae

Horticopia A-Z . CD-ROM database.

5.04

An evergreen palm - Arecaceae

Horticopia A-Z . CD-ROM database.

6.01

'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.'

http://translate.google.com/translate?hl=en&sl=fr&u=http://
www.france-palmier.com/especes-rustiques/washingtonia-robusta.htm&prev=/search%3Fq%3Dwashingtonia%2Brobusta%26hl%3
Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DG

6.02

(1) 'Seeds sometimes germinate in Western landscapes; I (Dr. Gilman) have not seen this in the eastern US.' (2) 'Washingtonia are hermaphrodites and only one specimen can produce viable seeds….The fresh seeds can germinate quickly, sometimes a few weeks after sowing, generally 1 to 3 months later.'

(1)Horticopia A-Z . CD-ROM database. (2)http://translate.google.com/translate?hl=en&sl=fr&u=http://
www.france-palmier.com/especes-rustiques/washingtonia-robusta.htm&prev=/search%3Fq%3Dwashingtonia%2Brobusta%26hl%3
Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DG

6.03

(1) Propagation: seed from isolated source; hybridizes readily. (2) '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).'

(1)http://ag.arizona.edu/pima/gardening/aridplants/Washingtonia_robusta
.htmlhttp://ag.arizona.edu/pima/gardening/aridplants/Washingtonia_robusta.html (2)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm

6.04

Propagates by self-seedling

http://www.tradeaplant.com/WhatPlant/ItemDetail.asp?WhatPlantIsThatID=63

6.05

(1)Pollen transfer by insects is frequent and diverse and involves flies (e.g., Nypa spp.), beetles (e.g., Orbignya, Bactris spp.), bees (e.g., Sabal palmetto, Iriartea spp.), and even moths (e.g., Bactris spp.) (Tomlinson 1979, Uhl and Dransfield 1987). [palms including Washingtonia] (2)Washingtonia appear to be almost entirely pollinated by insects and shed very little pollen.

(1)http://arboretum.arizona.edu/palms.htm (2)http://www.allegra.com/plant_glossary2.jsp?next=10&pletter=W

6.06

Washingtonia spp. are propagated by seeds (Brickell and Zuk 1997). Germination occurs two to four months after sowing (Jones 1995).

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

6.07

Don’t know.

7.01

'Fruits of Washingtonia spp. are small black drupes.' - No evidence that the propagules have any means of attachment.

7.02

(1)Attractive flowers or blooms. (2) 'This variety is excellent for larger gardens and lining streets and avenues.' (3)Washingtonia spp. are spread long distances through the horticulture trade

(1)Horticopia A-Z . CD-ROM database. (2)PlantMaster 5.5. 1999. CD-ROM database. V. 151 California version. (3)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm

7.03

seeds relatively large; no products

7.04

7.05

7.06

'On Maui, plants escape cultivation by seeds that are consumed and dispersed by fruit eating birds and possibly other animals. Birds that were observed in Washingtonia trees in Lahaina include common mynahs (Acridotheres tristis), java sparrows (Padda oryzivora), house finches (Carpodacus mexicanus), and house sparrows (Passer domesticus). Several mynahs were observed perched in trees consuming ripe fruits.'

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

7.07

possibly cached by rats?

7.08

(1)bird dispersal (2)Coyotes eat fruits from this palm and play an active role in their dispersal (Uhl and Dransfield 1987). (3)Dispersed by Taxidea taxus, Canis latrans, Procyon lotor

(1)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm (2)http://arboretum.arizona.edu/palms.htm (3)Felger, R. S. & E. Joyal. 1999. The palms (Arecaceae) of Sonora, Mexico. Aliso 18: 1–18.

8.01

Probably not, seeds relatively large. (1) '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.' (2) 'Fruit: pea-sized black/blue seed.' (3) Fruit 1/2" black berries. (4)Each fruit contains a single seed.

(1)http://translate.google.com/translate?hl=en&sl=fr&u=http://www.france-palmier.com/especes-rustiques/washingtonia-robusta.htm&prev=/search%3Fq%3Dwashingtonia%2Brobusta%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DG (2) http://ag.arizona.edu/pima/gardening/aridplants/Washingtonia_robusta.html (3)http://www.floridata.com/ref/w/wash_rob.cfm (4)http://www.crfg.org/pubs/ff/edible-palms.html

8.02

(1) 'Some seeds fail to germinate when provided with the necessary environmental factors for germination such as O2, H2O, light and suitable temperature. These seeds may contain germination inhibitors in certain parts of the seed. In this study, seed dormancy in Washingtonia robusta was studied with regard to the specific site of the dormancy mechanism and the influence of certain chemicals on the germination of these seeds. Results revealed that dormancy could be broken naturally by removing the outer seed coat or chemically by applying chemicals such as thiourea or cis -cinnamic acid. Dormancy could be restored by growth inhibitors present in the outer coat. It is concluded that the outer coat may contain germination inhibitors. The bioassay and use of HPLC apparatus revealed that inhibitor levels in the outer coat were relatively high, indicating that these inhibitors were responsible for dormancy in Washingtonia robusta seeds.' [in general, palm seeds are con

(1) Emam, M. M.; Khattab, H. E. 1997. Mechanism of dormancy in Washingtonia robusta seeds. Desert Institute Bulletin, Egypt, Vol.47, No.2, pp.379-390, 24 ref. (2)http://www.floridata.com/ref/w/wash_fil.cfm (3)http://palms.netfirms.com/palmseed.html (4)http://www.palmtreesofsc.com/palm3.htm (5)http://palmtreesdirect.com/washy.htm

8.03

spray Garlon 4 into apical bud

http://edis.ifas.ufl.edu/WG209

8.04

(1)"Physical control: Small plants can be dug up. Chain-sawing the palm at the base below the growing tip will also control it." [doesn't tolerate lopping] (2)Burning increased the yield of fruit crops, removed the dead shag from trunks for easier access to crops, and removed understory phreatophytes competing for water resources. [tolerates fire] 

(1)http://www.hear.org/starr/hiplants/reports/html/washingtonia_spp.htm (2)http://www.fs.fed.us/database/feis/plants/tree/wasfil/fire_ecology.html

8.05

Biological control: Not known.

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