Eye on Plants – Phyllostegia electra

Conservation Biologist Seana Walsh fondly recalls the scentless Hawaiian mint Phyllostegia electra not for its absent fragrance, but because it was the very first plant she collected on her first day of field work for NTBG.

Botanizing along with colleagues Steve Perlman and Merlin Edmonds, Seana brought seeds of the delicate P. electra back to the Garden’s Conservation and Horticulture Center where it was propagated and planted in the Montane Forest Display, allowing scientists to examine the rare plant without the expense and risk of undertaking an arduous journey.

Phyllostegia electra is endemic to the mesic and wet forests of Kauai and only rarely seen outside its habitat. Like other native Hawaiian plants, P. electra evolved in isolation and free of predators which is why it and Hawaii’s other 63 endemic mints lack the odorous oils that serve as a defense mechanism.

Critically Endangered

Furthermore, P. electra is assessed as Critically Endangered (CR) according to the IUCN Red List of Threatened Species and a focal species for achieving conservation objectives outlined in the Hawai‘i Strategy for Plant Conservation. It is not, however, protected by the Endangered Species Act.

With less than 50 known wild individuals growing in 15 subpopulations, P. electra was added to the University of Hawaii’s Plant Extinction Prevention Program (PEPP) [see related side bar on page 6]. Since early 2017, NTBG and PEPP have worked together to collect seeds and cuttings from known individuals, and search potential P. electra habitat for more.

As part of an ongoing genetic population study, NTBG is collaborating with Chicago Botanic Garden to better understand diversity in this species. Increased diversity means a more vigorous, robust gene pool and a better chance of survival for this species which is threatened by feral pigs, goats, rats, and even slugs and snails.

Propagated seeds or cuttings are outplanted into appropriate, protected, and managed habitat like the Upper Limahuli Preserve on Kauai’s north shore.

Seed Storage

Meanwhile, Seed Bank and Laboratory Manager Dustin Wolkis is experimenting with the seeds to determine how they respond to drying and cooling which will inform optimal storage methods. 

Phyllostegia electra fruits in the spring and cleaning seeds is a labor intensive process. After seeds are cleaned, Dustin tests initial exposure to liquid nitrogen to rapidly freeze seeds in order to avoid ice crystal formation (which can be lethal to cells) before transferring them into a -80°C freezer for long term storage. At this time, NTBG is the only facility in Hawai‘i testing liquid nitrogen for the cryopreservation of seeds.

A two-year grant from the Mohamed bin Zayed Species Conservation Fund helps pay for field botanists like Seana to fly out to remote habitat to collect plant material and for supplies like liquid nitrogen. By testing seeds for optimal storage conditions, the chances of saving the species from extinction greatly improve.

Dustin says, “This research, combined with ongoing collection, will reduce extinction risk and aid in the species’ recovery.” Collection, propagation, and the seed storage trials for this scentless Hawaiian mint continue.

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