Ornamentals and Flowers July 2012 OF-51 Naturalizing Orchids and the Hawaii Pacific Weed Risk Assessment System Patti Clifford and Kent Kobayashi Hawaii Invasive Species Council, CTAHR Department of Tropical Plant and Soil Sciences nvasive species are not only chang- recognized species. Orchids occur ing the composition of ecosystems; on all continents except Antarctica, theyI are also impacting ecosystem although there are species on some functionality and services. The orchid Antarctic islands. The distribution family, thought to be non-invasive, and abundance of the orchid family, now has species that are adapting however, tends to be centered in the to novel (newly formed) ecosystems tropics. Most orchids are epiphytes, globally. While scientists note that which grow on trees and shrubs, or orchids are a conservation concern, terrestrial, while some are lithophytes, because they are threatened by habi- growing on rocks, and a few are tat alteration, invasive species, and aquatic. Orchids range in size from climate change, there is limited dis- plants that could fit into a thimble to cussion of how the orchid family’s vines over 100 feet tall. adaptation to novel ecosystems might While orchids have a wide global promote the invasion of other species. distribution, they have evolved to Orchids are integral to ecological become ecologically specialized in connections in their native habitats, terms of their local habitat require- providing ecosystem services not yet ments. There are several ecological fully understood. This family interacts Arundinia graminifolia (photo: For- traits that have limited orchids to est and Kim Starr). with mychorrizal and pollinator ser- certain habitats. This rapidly evolving vices that connect many species and is family has formed unique interactions an important component of the ecosystem’s synergistic with both pollinators and mycorrhizal fungi, the latter of web. If this is the case, how can orchids be problematic, which have a symbiotic relationship with orchid roots. and why do gardeners and landscapers need to make The pollination trend in the orchid family is towards informed decisions when choosing one for the house, specialist pollinators. Orchids also require mycorrhizal garden, or landscape? While earlier data suggested fungi for seedling development, and in some species this that the orchid family is not invasive, recent research interaction is necessary into adulthood. Because of these indicates that the lag time, or sleeper effect; that is, the relationships, orchids are one of the most specialized time between introduction and invasiveness, might prove flowering plant families. This has tended to limit their otherwise. invasive tendencies. The orchid family (Orchidaceae) is considered by However, there is an emerging trend, or perhaps some scientists to contain the most species of all angio- evolutionary adaptation, within the orchid family. Some sperm (flowering) plant families, currently about 25,000 species, after introduction to an area outside of their na- Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in co- operation with the U.S. Department of Agriculture, under the Director/Dean, Cooperative Extension Service/CTAHR, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822. Copyright 2011, University of Hawai‘i. For reproduction and use permission, contact the CTAHR Office of Communication Services, [email protected], 808-956-7036. The university is an equal opportunity/affirmative action institution providing programs and services to the people of Hawai‘i without regard to race, sex, gender identity and expression, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or status as a covered veteran. Find CTAHR publications at www.ctahr.hawaii.edu/freepubs. UH–CTAHR Naturalizing Orchids and the Hawaii Pacific Weed Risk Assessment System OF-51 — July 2012 Dendrobium antennatum (photo: Danielle Frohlich and Dendrobium crumenatum (photo: Danielle Frohlich and Alex Lau). Alex Lau). tive distribution, are naturalizing and possibly becoming relationship of each species in the orchid family to the invasive. Naturalized species are able to reproduce and environment to which it is native is not well understood. sustain populations without human assistance. Invasive Orchids may perform a synergistic role within the ecosys- species also produce self-sustaining populations and tem and support many community relationships, though spread, at which point they may negatively impact human orchid researchers have yet to identify large-ecosystem health, the economy, or the environment. Some orchid services (e.g., the production of food and water, the species are naturalized in certain regions and invasive in control of climate and diseases, or the pollination of others. How can this adaptation happen? Daehler (1998) crops) within this family. Conservation efforts are us- noted that the Orchidaceae family is underrepresented ing the term “bioindicators” for orchids in their native in invasive families, and that there were at that time no ecosystems to express these species’ importance as an serious or widespread weeds among the estimated 17,500 early warning system to indicate the state of the eco- species in the family. Is this underrepresentation actual, system (Swarts and Dixon 2009). Because orchids are and due to ecological limitations, or is it merely based interconnected with pollinators and soil fungi, if either on the lack of orchid research? of these components of the ecosystem is disrupted, the If there is indeed an increase in naturalization in this orchid population can decline or disappear, and with it family, it may also be related to increased global trade the health of the ecosystem. Perhaps what we are see- and the introduction of more generalist species that can ing with the naturalization of orchids in the tropics is adapt to a variety of pollinators and mycorrhizal fungi an indication of multi-level changes in the composition, or other environmental conditions. Scientists and orchid structure, and function of ecosystems. Are naturalizing enthusiasts are seeing a number of orchid species and orchids “bioindicators” of severe stress in disturbed and hybrids naturalizing in temperate and tropical climates. natural ecosystems? Puerto Rico and Hawai‘i are at similar latitudes and As orchid enthusiasts, we can use these questions share some of these naturalizing species. Perhaps these and their answers to assist us in selecting orchids that species are some of the generalists within this family, not only evoke the vision of an exotic land but will stay newly introduced to the region, or they can adapt to the in cultivation and leave the natural world to the native novel ecosystems developing due in part to invasive spe- species. The invasive characteristics of orchid species cies impacts and/or global climate change. are still somewhat elusive; however, some characteristics The naturalization of orchids in disturbed and na- have been identified from naturalizing species. tive habitats is a concern for conservation efforts. The 2 UH–CTAHR Naturalizing Orchids and the Hawaii Pacific Weed Risk Assessment System OF-51 — July 2012 Dendrobium rhombeum (photo: Joel Lau). Spathoglottis plicata (photo: Forest and Kim Starr). Common characteristics of many naturalizing the establishment and spread of most naturalizing or inva- or invasive orchids (Adamowski 1999; Cohen and sive orchids (Adamowski 1999). However, Oeceoclades Ackerman 2009): maculate, an invasive orchid found throughout much • Rapid development from seed to flower (1–3 years of the neotropics, is expanding its distribution into not is short, but not uncommon) only disturbed sites but also old-growth forests with limited anthropogenic disturbance. This species may be • Autogamy (self-fertilization) negatively impacting two native orchid species in Puerto • Apomixes (seed production without fertilization) Rico (Cohen and Ackerman 2009). • Obligately outcrossing systems with deceptive pol- Scientists and orchid enthusiasts are also seeing lination system naturalizing orchids forming ecological connections with a variety of organisms. Liu and Pemberton (2010) • Tuber production (vegetative reproduction) have noted that the invasive orchid Cyrtopodium poly- • Abundant seed production phyllum is pollinated by an invasive bee, Centris ni- • High levels of phenotypic plasticity (observable tida, in Florida. In its native range, Cyrtopodium is physical or biochemical traits that can change with pollinated by two native species of the same genus, the environment) Centris tarsata and Centris labrosa. In Puerto Rico, Spathoglottis plicata has naturalized and occupies the • Wide ecological amplitudes (range of environmental same habitat as a native orchid, Bletia patula. A na- tolerance) tive weevil, Stethobaris polita, an orchid specialist, • Broad natural distribution is now negatively impacting the reproductive success Bletia • Disturbance tolerant (colonizes disturbed areas) of , due to its association with the increasingly abundant and widespread Spathoglottis. Emerging evi- dence also links orchids to non-orchid species in a plant Characteristics that might be associated with community through the mycohrrizal fungi associations naturalizing or invasive orchids: (Zettler et al. 2003). These complex interactions are de- • Associated with