Chapter Ten: Checklist of the Vascular Plants of Palau Craig M. Costion, David H. Lorence, Ann Hillmann Kitalong An essential element to any ethnobotanical project is a checklist for the region that is up to date with current taxonomy and botanical nomenclature. An outdated checklist could lead to confusion between names or unnecessary duplication of species concepts. As any plant enthusiast or specialist knows, a checklist of vascular plants for a particular bioregion is never final, but simply a snapshot in time of an ongoing process. This is especially true for tropical regions and areas of the Pacific, including Palau. Periodic publication of checklists is essential for tracking taxonomic updates to the native flora, and these are strengthened through systematic research on plant groups present in the region. Some species previously thought to be endemic are found to occur elsewhere while other species are revised to become single island endemics and scientific names are updated. This process is unavoidably slow. Until a complete modern Flora of Micronesia or Flora of Palau is completed, checklists provide a concise synthesis of these taxonomic changes, update our knowledge on the total number of species that occur on the islands, and provide a foundation for related research in ecology, ethnobotany, conservation and resource management. Although certainly some new taxa will turn up periodically, the vast bulk of work to be accomplished involves updating species concepts of the native flora. Since Palau is located just outside Southeast Asia, some of its native taxa are periodically revised in the Flora Malesiana series, some are treated in nearby regional floras, whilst others, particularly the endemics, are simply not covered in other regional based works. Earlier botanists Kanehira (1933), Fosberg & Sachet (1975a,b, 1977, 1980), and Fosberg et al. (1993) published partial treatments on the Flora of Micronesia that included complete species accounts. However, to date no comprehensive account of the plants of Palau, or the plants of Micronesia as a whole, exists. Guam, in the Southern Marianas remains the only Micronesian subregion with a complete flora (Stone 1970). In spite of these limitations, continuous progress on Palau’s vascular plant checklist in recent years has served as a focal point for research and exchange of knowledge on the plants of Palau. Many new records, discoveries, and insights have come to light over the past 10-12 years. Although Fosberg and his collaborators established a solid foundation for this list, there remain many unanswered questions. These have been and continue to be a primary driver for the additional studies on the Palauan and Micronesian flora. Methods This checklist of the vascular plants of Palau builds upon the recently published “Provisional Checklist of Plants of Palau” (Kitalong et al., 2008), which was largely based on the seminal works of Raymond Fosberg and his collaborators in their Geographical Checkists (Fosberg et al., 1979, 1982, 1987) and Flora of Micronesia series (Fosberg and Sachet 1975a,b, 1977, 1980; Fosberg et al., 1993). Other important contributions were derived from Lorence and Flynn’s (2018) Checklist of the Plants of Palau, Raulerson et al. (1997), Botanical Reconnaissance of the Proposed Compact – Impact Road Alignement on Babeldaob Island, Republic of Palau, Rinehart and Raulerson’s (2005) Orchids of Palau, Costion et al.’s (2009) Checklist of the endemic plants of Palau, Costion’s (2009) New and noteworthy plant records from Palau, and Costion and Lorence’s (2012) checklist of The Endemic Plants of Micronesia. Data on invasive species was incorporated from the US Forest Service (2007) Pacific Islands Ecosystems at Risk (PIER) list of the Invasive Plants of the Pacific Islands. Herbarium records supporting these works are held primarily at the Bernice P. Bishop Museum herbarium (BISH) in Honolulu, the U.S. National Herbarium (US) in Washington D.C., the National Tropical Botanic Garden (PTBG), Kauai, The New York Botanical Garden (NY), and the Belau National Museum herbarium (BNM). A digital photo library of the Bishop Museum specimens was compiled in 2005-2006. This is now in the process of being superseded by an online repository of scanned images of all specimens held in herbaria throughout the Pacific at the Consortium of Pacific Herbaria (2012) based at the Joseph F. Rock Herbarium at the University of Hawaii, Manoa. A separate database of the BISH and US specimens, compiled by Warren Wagner and Derral Herbst also served as an important reference in the compilation of this list. Our personal observations of these specimens, photographic records, and of the respective taxa in the field, and observations noted by aforementioned authors are all incorporated into this list. Current taxonomy of the names was checked through a general query of all taxa against The Plant List (2012) as a first step. Since The Plant List is not complete for many taxonomic groups, the results of this query were then assessed against relevant literature and our combined knowledge of the Palau and Micronesian flora. Plant names and authors follow usage on The Plant List and/or the International Plant Names Index (2012) except for cases where names were missing from these online resources and/or the current accepted name listed was not consistent with our assessment. The list is arranged in evolutionary order following APG III (THE ANGIOSPERM PHYLOGENY GROUP 2009) into Lycophytes, Pteridophytes, Gymnosperms, Basal Angiosperms, Monocots, and Eudicots. Families within these major vascular plant groups are arranged alphabetically. Native status of plants is indicated by the following abbreviations after each plant names: N = native; E = endemic; E(v) = endemic variety of a native species; I = introduced; I, N = introduced and naturalized, and I, X = introduced and invasive. The Flora of Palau Based upon this checklist, there are a total of 1,330 vascular plant known to occur in Palau. Out of this total nearly half, 630 species (47%) are introduced. At least 90 of these introduced species are considered to be invasive or potentially invasive weeds. Only a small percentage of these introduced plants however have successfully invaded Palau’s intact forests. Palau’s native flora remains the most diverse in Micronesia and has one of the highest native and endemic species richness values (species/km2) in the entire Pacific (Costion and Lorence 2012). There are approximately 698 vascular plants considered native to the Palau archipelago. Approximately 136 (19%) of these are considered endemic to Palau only, and an additional 12 species are considered endemic varieties of species with a larger geographic range. We emphasize the use of the word approximately because, as discussed above, the exact numbers regularly change as new taxonomic concepts are developed. Indeed, the native and/or endemic status of some of the species on our current list is likely to change within a few years of this publication. Regardless, we hope that this updated list for Palau will serve as a useful reference to people interested in Palau’s terrestrial biodiversity and its management and conservation. Taxon Palauan Name Status Lycophytes LYCOPODIACEAE Phlegmariurus phlegmaria (L.) T. Sen & U. Sen N Phlegmariurus squarrosus (G. Forst.) A. Love & D. Love N Palhinhaea cernua (L.) Frannco & Vasc. olcheuilabeab N SELAGINELLACEAE Selaginella ciliaris (Retz.) Spring N Selaginella dorsicola Hosok. meseumed E Selaginella palauensis Hosok. E Selaginella pseudovolkensii Hosok. meseumed E Selaginella tamariscina (P. Beauv.) Spring I Pteridophytes ATHYRIACEAE Diplazium melanocaulon Brack. N Diplazium sylvaticum (Bory) Sw. N ASPLENIACEAE Asplenium australasicum Hook. N Asplenium cuneatum Lam. N Asplenium laserpitiifolium Lam. N Asplenium nidus L. N Asplenium polyodon G. Forst. N Asplenium tenerum G. Forst. N BLECHNACEAE Blechnopsis orientalis (L.) C.Presl klorouikl N Stenochlaena palustris (Burm. f.) Bedd. N CYATHEACEAE Sphaeropteris lunulata (G.Forst.) R.M. Tryon cheluu N Sphaeropteris nigricans (Mett.) R.M. Tryon cheluu N DAVALLIACEAE Davallia angustata Wall. N Davallia denticulata (Burm. f.) Mett. ex Kuhn N Davallia embolostegia Copel. likerberdauch N Davallia pectinata Sm. N Davallia sessilifolia Blume N Davallia solida (G. Forst.) Sw. likerberdauch N Davallia heterophylla J. E. Sm. N Davallia repens (L.f.) Kuhns N DENNSTAEDTIACEAE Microlepia speluncae (L.) T. Moore N DRYOPTERIDACEAE Lomagramma sorbifolia (Willd.) ching N Dicranopteris linearis (Burm. f.) Underw. itouch N HYMENOPHYLLACEAE Abrodictyum dentatum Ebihara & K.Iwats. N Abrodictyum obscurum Ebihara & K.Iwats. N Abrodictyum setigerum Backh. ex T. Moore N Cephalomanes atrovirens C. Presl leam N Cephalomanes densinervium Copel. N Crepidomanes bipunctatum (Poir.) Copel. N Crepidomanes minutum (Blume) K. Iwats. N Didymoglossum bimarginatum (Bosch) Ebihara & K. Iwats. Didymoglossum motleyi Ebihara & K.Iwats. N Didymoglossum tahitense (Nadeaud) Ebihara & K.Iwats. N Crepidomanes humile (G. Forst.) Bosch N Hymenophyllum polyanthos (Sw.) Sw. N Hymenophyllum serrulatum C.Chr. N LINDSAEACEAE Lindsaea ensifolia Sw. N Lindsaea lobata Poir. N Lindsaea lucida Blume N Lindsaea obtusa J. Sm. ex Hook. N Lindsaea propinqua Hook. N Lindsaea repens var. lingulata K.U.Kramer N Lindsaea repens var. pectinata (Blume) Mett. ex Kuhn N Schizolegnia walkerae (Hook.) Alston N Sphenomeris chinensis (L.) Maxon N Tapeinidium amboynense (Hook.) C. Chr. N LOMARIOSIDACEAE Cyclopeltis cumingiana