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By Kassandra Jensen
Hiking through the cloud forests of Kauaʻi, you can find mounds of yellow, orange, and white lining the trail and black and red wrapping around trees and dripping off branches. In the mesic1 forests, you might glimpse a golden line scaling a tree or dull green cushions coating rocks. Even in the driest areas, furry, black objects can be found in the dirt. At the beach, salt spray hits the colorful speckles nestled into tiny holes of volcanic rock. Even in parking lots, the careful observer can discover bright green star-shaped growths thriving in concrete that is inhospitable to other plants.
From Hawaiʻi’s volcanic peaks and high elevation bogs to lowland and coastal areas, mosses and their relatives are found in almost every Hawaiian habitat. While often overlooked, I have been drawn to examine the ecological roles of these small plants.
Mosses and closely related liverworts and hornworts are collectively known as bryophytes, an ancient and diverse taxonomic group, comprising about 20,000 species2 worldwide. Bryophytes were among the earliest land plants and have played a crucial part in colonizing the planet. These extraordinary plants are haploid (containing one set of chromosomes), unlike flowering plants and animals which are diploid (containing two sets). It’s as if an unfertilized egg grew into a living, breathing being.
Bryophytes are unable to store water internally and are dependent on their environment for water. Their survival can be attributed to their ability to endure fluctuations in moisture availability by cycling in and out of periods of dormancy and activity. When rainfall and other forms of moisture are available, some species can absorb more than ten times their weight in water. Others can dry out to less than 10% of their body weight for long periods of time, able to resume normal function just minutes after hydration. Botanists have reported that some specimens kept in storage for over 50 years have “come back to life” after rehydration.
Left: Kassandra collecting moss. Photo by Ezikio Quintana. Right: Pyrrhobryum Spiniforme. Photo by Amanda Vernon.
Globally, bryophytes help maintain healthy ecosystems by preventing erosion, cycling nutrients, and fixing nitrogen through their associations with cyanobacteria (blue-green algae). Sphagnum moss-dominated peat bogs which have developed over thousands of years sequester more carbon than any other vegetation type in the world. Additionally, bryophytes act as forest “nursery sites” for flowering plant germination and seedling growth and can facilitate invertebrate life cycles in streams. Specifically, many moth-like caddisfly species rely on bryophytes to provide habitat and as a source of food in the form of leaf litter and other organisms.
In Hawai‘i, bryophytes have important associations with native plants and animals. The larvae of the endemic moth Hyposmocoma are consistently found within mats of the endemic moss Donrichardsia bartramii. These invertebrates and others like them may go on to pollinate plants or become food for larger animals.
Native flowering plant seedlings often sprout within mats of mosses and liverworts. In higher elevation forests, seedlings of ‘ōhi‘a3, ‘ōlapa4, and many epiphytic plants are often exclusively found in patches of moss.
Hawaiian forest birds, such as the ‘elepaio5, use the reproductive structures of bryophytes of the native fire-moss6 to build their nests. Bryophytes also act as refuges in harsh environments, such as Haleakalā crater on Maui, where vascular plants are more likely to be found growing in biocrusts7 composed of different species of the alpine moss Grimmia and lichens.
I was drawn to bryophytes by the important but under-appreciated role of Hawaiian mosses. On my first day working at Limahuli Garden and Preserve, I passed a fallen log covered in a vibrant mat of orange, green, and yellow. I realized there was a small but dynamic world that deserved to be explored. This curiosity, fostered by support from my NTBG colleagues, led me to graduate school where I began to study bryology8, exploring what drives their abundance and how they connect with native invertebrates and flowering plants.
Left: Kassandra working in Limahuli stream. Photo by Brendan Stogner. Right: A lacewing among liverworts. Photo by Ken Wood.
My field observations have taught me how much there is to learn about bryophyte ecology in Hawai‘i. While bryology is understudied as a whole, the field of bryophyte ecology is even less understood, with only five published studies to date in Hawai‘i. This lack of foundational knowledge highlights the need for updated resources to help researchers and conservationists recognize and understand these plants.
The Manual of Hawaiian Mosses by Edwin B. Bartram was published in 1933 and remains the only comprehensive moss key9 in use. Until recently, there was no key for liverworts or hornworts in Hawai‘i. Fortunately, today there is a resurgence of interest in these special plants.
NTBG researchers Tim Flynn and Amanda Vernon are working to make bryophytes more accessible to the public. Starting with a field guide, they are showcasing 30 common Hawaiian mosses for a non-specialist audience. Once their guide is published this fall, they will create a tool for identifying moss characteristics, updating the 92-year-old manual to a digital version that will help pair specific moss characteristics with selected traits. Additionally, NTBG has been working to digitize all herbarium collections, including the bryophytes, which can be viewed using the herbarium search directory online.
Private researchers, Dr. Virginia Freire and Dr. Emmet Judziewicz, have been working in Hawai‘i over the last several years to explore and research liverworts and hornworts. Through a partnership with NTBG, they have identified many liverworts and hornworts that have been stored in herbaria for years but remain unidentified. Their research has made important contributions, including the identification of both new species and a genus of liverwort and the publication of the first of their multi-volume manual of liverworts.
Left: Native plants growing out of moss in Kanaele Bog, Kauaʻi. Photo by Kassandra Jensen. Right: Philonotis turneriana. Photo by Ken Wood.
Over the last five years, NTBG and Bishop Museum have co-hosted multiple moss workshops that have helped educate bryophyte conservationists and enthusiasts. Unfortunately, there is relatively little information about Hawaiian names and uses for bryophytes in institutional literature. At least one moss has a specific name: mākole mākō pi‘i10,. The word limu, although more commonly associated with the algae found in the ocean, is the Hawaiian word for bryophytes as well.
There is certainly far more Indigenous knowledge in Hawaiʻi about bryophytes that could provide insight into their ecological roles and cultural significance, but it remains undocumented in institutional literature. These resilient plants can withstand the harshest of environments and support countless other species. Clearly, we still have much to learn about bryophytes. The more we understand them, the better equipped we will be to steward our environment.
Kassandra worked with NTBG as a Kupu program member (2020-2022) and as Limahuli Garden and Preserve staff (2021-2023). Currently, she is an independent researcher on Kaua‘i.
[1] Receiving moderate rainfall
[2] Bryophytes are comprised of mosses (60%), liverworts (36%), and hornworts (4%).
[3] Metrosideros spp.
[4] Cheirodendron spp.
[5] Chasiempis sandwichensis
[6] Pyrrhobryum spiniforme
[7] Thin layers of soil rich in tiny living organisms
[8] Study of bryophytes
[9] A book used to distinguish plants based on observable traits
[10] Thuidium cymbifolium
