Edible and Medicinal Seaweeds of North America A Comprehensive Guide to Healing and Nutritive Ocean Plants
, by Greenwood, Tasha
- ISBN: 9781635868708 | 163586870X
- Cover: Paperback
- Copyright: 1/20/2026
Tasha Greenwood (they/them) is an educator and herbalist with a background in marine science. They are a co-owner of Mxed Greens, an herbal apothecary in Northampton, MA, where they teach workshops in collaboration with local colleges and farms. Greenwood writes monographs for the online platform HerbMentor, LOAM magazine, and the Journal of the American Herbalists Guild. They hold a BS in environmental science with a focus on marine ecology and maritime studies from Northeastern University and received clinical herbalist training at the Hudson Valley School of Herbal Studies, Milk & Honey Herbs Apprenticeship, the California School of Herbal Studies, and the Vermont Center for Integrative Herbalism.
Proposed Table of Contents
1. Introduction (with Sargassum) - personal context, how to use this book
2. Botany Basics
Each section in this chapter is organized around a different species of seaweed. There is a contextual narrative about a location where I have observed or harvested this seaweed, then a deep dive on the specific botany, history, and traditional medicinal use of this species. Each chapter ends with Herbal Medicine Preparations and Culinary Recipes that include that seaweed along with bioregional produce, proteins, and herbs. Spread across the chapters are also vignettes on ‘Tasting Notes’ (salty, umami, bitter, sweet) that apply to seaweeds, ‘Phytochemistry Features’ detailing compounds in the plants that give them medicinal action as well as current clinical research, and ‘Intertidal Interviews’ with seaweed harvesters, farmers, and ocean stewards who are connected to these ecosystems. Order of chapters is flexible. *All recipes have not been filled in yet - all may be developed by me, or in conjunction with another recipe developer*
A. Chondrus crispus/Irish Moss (Nahant, MA)
Small Meals + Sides
Main Dishes
Medicinal Benefits of Seaweed
Seaweeds are incredibly nutrient dense, with up to ten times the vitamin and mineral concentrations of land plants living in the same ecosystem. Seaweeds are particularly high in A, C, and B vitamins, as well as iodine, calcium, potassium, magnesium, iron, and manganese. All are key to tissue form and function within the body, and consuming seaweed is an easy way to bolster the body in times of illness, stress, or convalescence. The high levels of antioxidants in seaweeds reduce cell damage from oxidative stress. There is a reason why so many bath and body products contain seaweed extracts - they really shine for rejuvenating and protecting skin and external tissues. The following paragraphs are an overview of additional medicinal benefits of each seaweed grouping (greens/Chlorophyta, reds/Rhodophyta, and brown/Phaeophyta.)
Green seaweeds are primarily utilized as a nutritive food. I think of them like a good romaine lettuce - delicious with a nice texture, but not as nutrient dense and complex as spinach or nettles. For this reason, I think that sea lettuce can be great as a salt and mineral source in an electrolyte replacement switchel, but not so much for other medicinal preparations.
Red seaweeds contain polysaccharides called carrageenans that form gels when extracted in water. These gels are demulcent and emollient, soothing to tissues internally and externally. Carrageenan has a long history of use as a digestive support, to ease dyspepsia much in the same way as we use marshmallow root mucilage. There is also evidence for carrageenan gel promoting metabolic regulation by both slowing the absorption of sugars and providing necessary soluble fiber. It’s also great antispasmodic and expectorant for coughs and respiratory congestion that often come with living in the cool, damp climates of the shores where these seaweeds grow. Carrageenan also exhibits some interesting anti-viral properties against HPV and HSV-1; and is currently being studied against SARS COVID-19.
Brown seaweeds contain the polysaccharide fucoidan, which has been extensively studied. Brown seaweeds are a powerful adjunct therapeutic for treating diabetes and metabolic syndrome. Similar to carrageenans, fucoidans have demonstrated antiviral activity against HIV, Hep-B, and Influenza in vitro, and hopefully clinical trials are on the way. Likewise, even though clinical trials have not been published yet, brown seaweeds have extensive history of use to treat cancers in Traditional Chinese Medicine and in vitro studies corroborate this. Brown seaweeds contain the highest concentrations of iodine and are fantastic support for hypothyroidism. While not a replacement for thyroid hormone treatments (i.e. levothyroxine), the extra boost of iodine can significantly improve thyroid function in those with borderline hypothyroidism and improve medication efficacy for those with clinical hypothyroidism.
When consuming seaweeds for culinary or medicinal use, quantity and frequency are important. Because seaweeds are so nutrient-dense, you don’t want to just eat a huge portion of seaweed once in a while. That is akin to storm runoff washing excess agriculture fertilizer into a body of water, resulting in a massive algae bloom and eutrophication, and an unbalanced ecosystem that takes time to recalibrate. In order to get the most benefits from seaweed, the ideal is to eat small amounts, routinely. This moderated approach allows your body to actually take in and use the nutrients effectively without being flooded in a boom and bust cycle. The same is true for internal medicinal applications - small doses frequently allows the body to use the carrageenans or fucoidans to the most effect.
Medicinal Recipes
*note that many of these could also be placed in a ‘nutritive’ category of medicinal benefits and some of these have been mentioned in the culinary recipes section above due to significant overlap*
Topical Preparations
1. Introduction (with Sargassum) - personal context, how to use this book
2. Botany Basics
- Seaweeds vs Land Plants (structure/function)
- Phylogenetic groupings (Green/Red/Brown)
- Seaweed reproduction + growth habits
- Intertidal zone overview (characteristics of this environment, shifts with latitude, seaweed aggregation by species across the intertidal zone)
- Seaweeds in broader ecological scope (role as photosynthesizers, habitat builders, keystone species in food webs. Seaweed shifts as waters warm + sea levels rise, mariculture as a booming field for various applications)
- Harvesting/Foraging instructions + protocols, how to dry + preserve seaweed
- Notes on ethical wildcrafting + foraging, the Honorable Harvest (Robin Wall Kimmerer)
- Seaweeds
Each section in this chapter is organized around a different species of seaweed. There is a contextual narrative about a location where I have observed or harvested this seaweed, then a deep dive on the specific botany, history, and traditional medicinal use of this species. Each chapter ends with Herbal Medicine Preparations and Culinary Recipes that include that seaweed along with bioregional produce, proteins, and herbs. Spread across the chapters are also vignettes on ‘Tasting Notes’ (salty, umami, bitter, sweet) that apply to seaweeds, ‘Phytochemistry Features’ detailing compounds in the plants that give them medicinal action as well as current clinical research, and ‘Intertidal Interviews’ with seaweed harvesters, farmers, and ocean stewards who are connected to these ecosystems. Order of chapters is flexible. *All recipes have not been filled in yet - all may be developed by me, or in conjunction with another recipe developer*
A. Chondrus crispus/Irish Moss (Nahant, MA)
- Context: Part of my college experience studying marine botany, my first true introduction to the tidepools of the rocky New England shore.
- Phytochemistry Feature: Carrageenan
- Interview with herbalist Lauren Giambrone about using irish moss
- Culinary Recipes featuring: irish moss
- Herbal Medicine Preparations: Irish moss carrageenan for HPV, COVID-19, Irish moss carrageenan cough syrup.
- Context: another place I spent much of my early 20s, both in school and working.
- Interview: Wampanoag Tribal Member (perhaps Ms. Tavares Avant, but there other folks too who know ethnobotanical uses of seaweed and continue to steward patches on the Cape and Martha’s Vineyard)
- Phytochemistry Feature: Ascophyllan
- Culinary Recipes featuring: cape gooseberries, kelp, Rosa rugosa, cranberries, squash
- Context: two coasts I have lived on and harvested seaweed from. The coasts are very different from each other but united by kelp.
- Tasting Notes: Sweet
- Interview: Sarah Thorpe from Swell Seaweed Co. (Maine)
- Interview with Seagrove Kelp (Alaska)
- Culinary Recipes featuring: kelps!
- Context: the link between the ecosystems of the northern gulf of Maine and the places where many of my ancestors are from in Northern Europe. Winged kelp unites them.
- Phytochemistry Feature: Fucoidans, Seaweed and metabolic syndrome
- Interview with Nautical Farms (Maine)
- Interview with Ironbound Island Seaweed (Maine)
- Interview with Atlantic Sea Farms (Maine)
- Culinary Recipes featuring alaria, wild greens, clams
- Context: Lubec research station, herbarium pressings, learning to like bitter flavored foods.
- Tasting Notes: Bitter
- Interview with Micah Woodcock of Atlantic Holdfast Seaweeds (Maine)
- Interview with Cup of Sea (Maine)
- Culinary Recipes feat: dulse, potatoes
- Context: A body of water that I lived and worked on aboard a tallship. An ecology very linked to urban places and cities, but where seaweeds are still abundant.
- Phytochemistry Feature: Iodine + the Thyroid (& how to use bladderwrack medicinally as thyroid support)
- Interview: Stonington Kelp Co (CT)
- Herbal medicine: preparations for taking bladderwrack as a thyroid support (capsules, tea, infusions
- Context: the first seaweed that I ate straight out the tidepool without any cooking or preparation and it changed my culinary world.
- Tasting Notes: Umami
- Culinary Recipes featuring: Cystoseira, Bull Kelp
- Herbal Medicine Preparations: seaweed ferments and the gut microbiome
- Context: Where I lived for a year of herb school, and the start of COVID.
- Interview with Autumn Summers or her connections.
- Phytochemistry Feature: Porphyran
- Culinary Recipes feat: nori and laver, CA local produce
- Context: continuation of pacific coast experiences, seaweed harvesting in the tidepools and leaning on their cooling, soothing properties during the intense fire season of summer 2020.
- Herbal Medicine Preparation: Seaweed cream (topical)
- Context: I lived in Hawaii for various short stints, and sailed there as well. Indigenous use of seaweeds. The cultural context of this Pacific island as a meeting place of asian immigrants, white settlers, and indigenous communities.
- Tasting Notes: Salt
- Phytochemistry Feature: Chlorophyll
- Recipes feat: sea lettuce
- Context: grows prolifically in the Caribbean, easily available in Southern Florida markets because of geographic proximity and demographics of Caribbean immigrants. Has gained huge interest in the wellness market in the last 5 years.
- Phytochemistry Feature: Agar
- Interview with a sea moss company
- Recipes feat. agar as a thickener or gelatin alternative
- Herbal medicine: immune boosting elderberry syrup gummies set with agar
- Hijiki, Arame, Caulerpa (sea grapes) - these are found on coasts of Japan, China, Korea. Analogues exist on the coasts of North America, but not the exact same species.
- A few recipes featuring each of these.
Preliminary Recipe List
I divided these into general recipe categories rather than by seaweed type so you can get a sense of the breadth of recipes represented overall. I generally cook vegetarian + seafood. My cooking revolves around quality herbs and produce, and bright spice flavors. I love a pop of coriander or cardamom, the zesty play of citrus and chili, layers of ginger and garlic, and creative sweet/savory combos. Texture is a crucial consideration when cooking with whole seaweeds, balancing the unique mouthfeel of sea vegetables with other, perhaps more familiar, ingredients.
Sauces/Condiments
- Seaweed and herb infused salts (ie furikake)
- Spring tonic vinegar with herbs and seaweeds
- Seaweed infused fire cider
- Seaweed kimchi
- Pickled seaweed (cystoseira, kelp, and others)
- Seaweed hot sauce
- Seaweed infused vinaigrette
- Seaweed pesto
- Broths + Soups
- Broths/Soups- Dashi with kombu and mushrooms
- Broths/Soups - Miso with wakame and tofu
- Broths/soups - traditional veggie or meat stock with seaweed
- Broths/soups - Pho with wakame or Alaria
- Broths/ soups - Immune support broth with seaweeds, reishi, astragalus
- Broths/Soups- Seaweed + herb instant bouillon mix for quick broths
- Congee made with seaweed veg broth or with dashi
- Tidepool Beans in the crockpot (with rockweed or kelp)
- One pot rice and beans with sea lettuce
- Seaweed boule (could be sourdough or traditional yeasted dough)
- Savory seaweed cornbread or corn muffins
- Sweet potato, scallion & seaweed savory galette
Small Meals + Sides
- Sushi rolls w plum and avocado (nori)
- Fresh Spring rolls with kelp noodles and herbs
- Cold seaweed salad with wakame and jicama
- Seaweed miso maple roasted radishes
- Sea moss + fruit smoothies
Main Dishes
- Katsu curry with dulse
- Macadamia nut ‘hollandaise’ sauce with sea lettuce or dulse over roasted vegetables
- Seaweed clam bake (in the sand… or on your stove)
- Burdock and seaweed pasta with arame
- Seaweed wrapped baked fish
- Peanut noodles with sea lettuce and dulse
- Blancmange pudding (with irish moss)
- Dried fruit + rockweed infused chocolate
- Coconut and passionfruit haupia (with agar)
- Seamoss jam or marmalade
- Chocolate seaweed truffles (with bladderwrack)
Medicinal Benefits of Seaweed
Seaweeds are incredibly nutrient dense, with up to ten times the vitamin and mineral concentrations of land plants living in the same ecosystem. Seaweeds are particularly high in A, C, and B vitamins, as well as iodine, calcium, potassium, magnesium, iron, and manganese. All are key to tissue form and function within the body, and consuming seaweed is an easy way to bolster the body in times of illness, stress, or convalescence. The high levels of antioxidants in seaweeds reduce cell damage from oxidative stress. There is a reason why so many bath and body products contain seaweed extracts - they really shine for rejuvenating and protecting skin and external tissues. The following paragraphs are an overview of additional medicinal benefits of each seaweed grouping (greens/Chlorophyta, reds/Rhodophyta, and brown/Phaeophyta.)
Green seaweeds are primarily utilized as a nutritive food. I think of them like a good romaine lettuce - delicious with a nice texture, but not as nutrient dense and complex as spinach or nettles. For this reason, I think that sea lettuce can be great as a salt and mineral source in an electrolyte replacement switchel, but not so much for other medicinal preparations.
Red seaweeds contain polysaccharides called carrageenans that form gels when extracted in water. These gels are demulcent and emollient, soothing to tissues internally and externally. Carrageenan has a long history of use as a digestive support, to ease dyspepsia much in the same way as we use marshmallow root mucilage. There is also evidence for carrageenan gel promoting metabolic regulation by both slowing the absorption of sugars and providing necessary soluble fiber. It’s also great antispasmodic and expectorant for coughs and respiratory congestion that often come with living in the cool, damp climates of the shores where these seaweeds grow. Carrageenan also exhibits some interesting anti-viral properties against HPV and HSV-1; and is currently being studied against SARS COVID-19.
Brown seaweeds contain the polysaccharide fucoidan, which has been extensively studied. Brown seaweeds are a powerful adjunct therapeutic for treating diabetes and metabolic syndrome. Similar to carrageenans, fucoidans have demonstrated antiviral activity against HIV, Hep-B, and Influenza in vitro, and hopefully clinical trials are on the way. Likewise, even though clinical trials have not been published yet, brown seaweeds have extensive history of use to treat cancers in Traditional Chinese Medicine and in vitro studies corroborate this. Brown seaweeds contain the highest concentrations of iodine and are fantastic support for hypothyroidism. While not a replacement for thyroid hormone treatments (i.e. levothyroxine), the extra boost of iodine can significantly improve thyroid function in those with borderline hypothyroidism and improve medication efficacy for those with clinical hypothyroidism.
When consuming seaweeds for culinary or medicinal use, quantity and frequency are important. Because seaweeds are so nutrient-dense, you don’t want to just eat a huge portion of seaweed once in a while. That is akin to storm runoff washing excess agriculture fertilizer into a body of water, resulting in a massive algae bloom and eutrophication, and an unbalanced ecosystem that takes time to recalibrate. In order to get the most benefits from seaweed, the ideal is to eat small amounts, routinely. This moderated approach allows your body to actually take in and use the nutrients effectively without being flooded in a boom and bust cycle. The same is true for internal medicinal applications - small doses frequently allows the body to use the carrageenans or fucoidans to the most effect.
Medicinal Recipes
*note that many of these could also be placed in a ‘nutritive’ category of medicinal benefits and some of these have been mentioned in the culinary recipes section above due to significant overlap*
Topical Preparations
- Seaweed skin cream (with Irish moss or Mazaella spp)
- Seaweed facemask (with kelp)
- Seaweed + clay for muscle pain (with kelp)
- Seaweed bath soak
- Irish moss personal lubricant
- Spring tonic vinegar with herbs and seaweed (with kelp, dulse, or sea lettuce)
- Seaweed fire cider
- Irish moss tincture
- Elderberry gummies gelled with agar
- Bladderwrack tea blends
- Bladderwrack chocolate truffles for thyroid support
- Irish moss cough syrup / respiratory tonic
- Seaweed kimchi for prebiotic and probiotic GI support
- Irish moss or Caribbean sea moss gel smoothies for digestive support
- Broth blends for GI support, immune support, and general convalescence feat various seaweeds other medicinal herbs (ie reishi, astragalus, codonopsis, sage, rosemary, hawthorn)
- Seaweed and ginger electrolyte switchel
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