The Hawaiian Endemic `Āla`a (Planchonella sandwicensis) Represents Two Distinct Taxonomic Entities
J. Christopher Havran (Campbell University), Stephan Nylinder (University Gothenburg), and Ulf Swenson (Swedish Museum of Natural History)
Background:
Planchonella (Sapotaceae) in Hawai`i is currently recognized by the polymorphic endemic P. sandwicensis (`Āla`a). `Āla`a has previously been separated into 6 species and multiple forms.
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Swenson et al. (2019) recently conducted a global phylogeny of Planchonella which revealed that the genus in Hawai`i is represented by two well-supported clades distinguished by fruit color.
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Purpose:
We conducted a thorough molecular and morphological study of endemic Hawaiian Planchonella to further define boundaries between distinct species in Hawai`i.
Endemic Hawaiian Planchonella
Background:
Planchonella (Sapotaceae) in Hawai`i is currently recognized by the polymorphic endemic P. sandwicensis (`Āla`a). `Āla`a has previously been separated into 6 species and multiple forms.
Swenson et al. (2019) recently conducted a global phylogeny of Planchonella which revealed that the genus in Hawai`i is represented by two well-supported clades distinguished by fruit color.
Purpose:
We conducted a thorough molecular and morphological study of endemic Hawaiian Planchonella to further define boundaries between distinct species in Hawai`i.
Forty-two Planchonella specimens from across it`s range in Hawai`i were incorporated into the current survey. For each, rpb2, ITS, and ETS regions were sequenced. Over 50 reproductive and vegetative traits, if available, were scored for each specimen.
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Methods
Forty-two Planchonella specimens from across it`s range in Hawai`i were incorporated into the current survey. For each, rpb2, ITS, and ETS regions were sequenced. Over 50 reproductive and vegetative traits, if available, were scored for each specimen.
Our expanded phylogeny supports the two-clade phylogeny earlier reported by Swenson et al. (2019). Leaf, pedicel, corolla, and fruit characteristics contribute to the separation between the two clades. The purple-fruited clade is distributed on Kaua`i, O`ahu, and Maui Nui while the yellow clade is distributed on all islands, but seems to be rare on Kaua`i. The purple-fruited clade is composed of two well-supported subclades on Maui Nui and Kaua`i/O`ahu. There is not a morphological difference between these two subcclades of purple-fruited Planchonella.
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Revised Phylogeny
Our expanded phylogeny supports the two-clade phylogeny earlier reported by Swenson et al. (2019). Leaf, pedicel, corolla, and fruit characteristics contribute to the separation between the two clades. The purple-fruited clade is distributed on Kaua`i, O`ahu, and Maui Nui while the yellow clade is distributed on all islands, but seems to be rare on Kaua`i. The purple-fruited clade is composed of two well-supported subclades on Maui Nui and Kaua`i/O`ahu. There is not a morphological difference between these two subcclades of purple-fruited Planchonella.
Our results clearly support the presence of two endemic Planchonella species in Hawai`i. The boundaries between these species will primarily follow four morphological characters:
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The purple-fruited clade corresponds to Planchonella sandwicensis while the yellow-fruited clade corresponds to the type material of P. spathulata, currently in synonymy with P. sandwicensis. Morphology of P. spathulata is very variable across its range, even within islands like Maui, but there is no molecular or morphological support for additional subdivision of the species.
Amended descriptions of Planchonella sandwicensis and P. spathulata are currently being drafted. It is our hope that this reevaluation of Hawaiian Planchonella will establish a strong foundation for the understanding of species differences within this genus to aid and inform future conservation efforts.
New Species Boundaries
Our results clearly support the presence of two endemic Planchonella species in Hawai`i. The boundaries between these species will primarily follow four morphological characters:
The purple-fruited clade corresponds to Planchonella sandwicensis while the yellow-fruited clade corresponds to the type material of P. spathulata, currently in synonymy with P. sandwicensis. Morphology of P. spathulata is very variable across its range, even within islands like Maui, but there is no molecular or morphological support for additional subdivision of the species.
Amended descriptions of Planchonella sandwicensis and P. spathulata are currently being drafted. It is our hope that this reevaluation of Hawaiian Planchonella will establish a strong foundation for the understanding of species differences within this genus to aid and inform future conservation efforts.
Curators at BISH and PTBG herbaria kindly gave access to their collections. Collections made in Hawaii became possible through permits granted through the Hawaii Department of Land and Natural Resources, Division of Forestry and Wildlife (KPI-2015-48, MDF-052215A, ODF-041715R1, 13-209-5), Division of State Parks (K2015- 320cc), and Parker Ranch (permit 150121), as well as permissions from Kualoa Ranch, The Department of Hawaiian Home Lands, Kamehameha Schools, The National Tropical Botanical Garden, The Lyon Arboretum, The Nature Conservancy of Hawaii-Molokai Branch, The Amy B.H. Greenwell Ethnobotanical Garden, and Waimea Valley Garden. Elizabeth Willett-Dean assisted on morphological studies. Field support was provided by Kailie Aina, Mahie Atay, Nicolai Barca, Keahi Bustamente, Joseph Camara, Marian Chau, Susan Ching-Harbin, Rikki Cooke, Merlin Edmonds, William Haase, Bil Haus, Russell Kallstrom, Lucas Luehrs, Christian Lum, Art Medeiros, Hank Oppenheimer, David Orr, Laurent Pool, Alex Quintana, Elliott Parsons, Richard Pender, Robert Pitts, Maggie Sporck-Koehler, Kobey Togikawa, Vigge Ulfsson, and Patti Welton.
