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The Hawaiian Islands were first settled by Polynesians around 1200 CE.¹ The “discovery” of Hawai'i, and with it its flora, fauna, people, and customs, generally is attributed to the British explorer James Cook (1728–1779) in 1778, even though it has been argued that the Spanish captain Ruy López de Villalobos may have been the first European to set foot on Hawai'i in the 16th century.²

This article reviews the traditional and modern uses of plants in the genus Pipturus Wedd. (Urticaceae), which occur from the Mascarene Islands in the Indian Ocean to the South Pacific via Austro-Malaysia. Specifically, this article focuses on four endemic Pipturus species that are collectively known as “māmaki” and found on the Hawaiian Islands.* Māmaki is commonly used for fiber, and its use in local native traditional medicine is documented in locations throughout the genus’ vast range. In recent years, commercial cultivation, primarily of P. albidus (Hook. & Arn.) A.Gray ex H.Mann, has yielded local tea and beverage products that are now marketed throughout the United States.^3,4 Apart from historical accounts, there is a paucity of data in the public domain on Pipturus chemistry and pharmacology, leaving traditional medicinal uses largely uncorroborated.⁴ It is hoped that the data presented in this article may trigger further biopharmaceutical research and development of these interesting botanicals.

Discovery and Nomenclature

What is known today as the genus Pipturus emerged from several nomenclatural revisions of the Urticaceae family. French botanist Antoine Laurent de Jussieu (1748–1836) grouped multiple genera under Urticaceae in 1789 — including Artocarpus Forst., Boehmeria Jacq., Cannabis L., Cecropia L., Elatostema Forst., Forsskaolea L., Humulus L., Morus L., Parietaria L., ProcrisCommers., Pteranthus Forssk., Theligonum L., and Urtica L. — and is attributed with the authority of the family.⁵

French botanist Charles Gaudichaud-Beaupré (1789–1854) revised the Urticaceae family in French naval officer Louis de Freycinet’s (1779–1842) Voyage autour du monde, entrepris par ordre du roi. Exécuté sur les corvettes de S.M. l’Uranie et la Physicienne, pendant les années 1817, 1818, 1819 et 1820.⁶ It may be here where the first mention of “māmaki” was made and attributed to members of the genera Boehmeria and Procris, which occur on the Sandwich Islands (Hawai'i). De Freycinet’s publication also may have included the first description of Boehmeria dioica, which British botanists William Jackson Hooker (1785–1865) and George Arnott Walker-Arnott (1799–1868) redescribed and placed in the genus Boehmeria (as Boehmeria albida Hook. & Arn.) in The Botany Of Captain Beechey’s Voyage.⁷

Further revising the Urticaceae family, Anglo-French botanist Hugh Algernon Weddell (1819–1877) introduced the genus Pipturus in 1854⁸ and included B. albida as Pipturus taitensis Wedd. Later, American botanist Horace Mann Jr. (1844–1868) corrected Weddell, noting that “the name Taitensis, given by Weddell, is wholly inappropriate for a plant entirely unknown to Tahiti.” Mann also compared his own collection with that of American botanist Asa Gray (1810–1888) from the United States Exploring Expedition under American explorer Charles Wilkes (1798–1877).^9,10 Weddell’s treatment of the Urticaceae family in French-Swiss botanist Alphonse Pyramus de Candolle’s (1806–1893) Prodromus systematis naturalis regni vegetabilis lists eight species of Pipturus, including P. albidus under its hitherto accepted name.¹¹

It was a different species of the genus, Pipturus argenteus Wedd. — initially classified as Urtica argentea G. Forst. — that was first mentioned in the literature. The journal of Cook’s first voyage (1768–1771) described “a frutescent nettle; the urtica argentea, called Erowa” as growing on Otaheite (Tahiti). “[A]nd of the bark of the Erowa, a kind of nettle which grows in the mountains, and is therefore rather scarce, they make the best fishing lines in the world,” the journal noted.¹² The plant was described by Swedish naturalist Daniel Solander (1733–1782), sketched by Scottish artist Sydney Parkinson (1745–1771), and its Latin binomial appropriated by German naturalist Georg Forster (1754–1794) as his own.¹³ English botanist and naturalist Sir Joseph Banks (1743–1820), who accompanied Cook on his first voyage, included a color engraving of P. argenteus (Urtica argentea), which was based on Parkinson’s depiction, in Banks’ Florilegium (plate 656, 1769, Figure 1).

Whether Pipturus species were collected on Hawai'i during Cook’s third voyage in 1779 is uncertain, as the botanical collection made by David Nelson (d. 1789) in a five-day expedition in which he attempted to climb Mauna Loa (Hawai'i) is poorly documented.¹²Nelson left no journal, and the approximately 130 specimens he collected were deposited in the British Museum of Natural History without further ado.^14,15 An effort was made to identify Nelson’s specimens, but māmaki was not among them.¹⁶

Multiple authors agree that Pipturus on Hawai'i is highly variable and difficult to classify.^17-20 Austrian-American botanist Joseph Francis Rock (1884–1962) put it into even more drastic terms, stating that P. albidus “is a most variable species, and if one should undertake to separate the various forms, one would have to name individual trees.”¹⁸ According to The World Flora Online database, the genus Pipturus includes a total of 34 species. In a 1970 paper, Nicharat and Gillett stated that the genus contained approximately 49 recognized species, 21 of which were said to occur on Hawai'i. They also noted that all species were members of the section Mamakea, which are characterized by sessile flowers in axillary clusters (as opposed to elongated spikes in the section Pipturus).²¹

Wagner et al (1990) reduced the number of distinct Pipturus species to four (all endemic to the islands of Hawai'i), relegating formerly recognized species into synonyms (Table 1).²² At the time of Wagner et al’s writing, P. albidus occurred on all Hawaiian islands except Ni‘ihau and Kaho‘olawe; P. forbesii occurred on Maui only; and P. kauaiensis and P. ruber occurred on Kaua‘i only. Due to commercialization efforts, this is likely no longer the case. Both Wagner et al and Nicharat and Gillett agree that the Hawaiian Pipturus species all may have evolved from a single colonizer. Nicharat and Gillett also described ready hybridization, which further complicates accurate botanical identification and attribution, especially as the species no longer are separated geographically.²¹Danish botanist Ib Friis, in his 1993 treatment of the Urticaceae family, pointed out the need for a revision of the genus.²³

Welch (1998) contested the endemism of P. albidus and recorded it as present in the Society Islands (specifically, Tahiti),²⁴ which is supported by French botanist Emmanuel Drake del Castillo (1893),²⁵ even though the accounts appear not to be overly reliable. In fact, Skottsberg (1932) had already addressed reports of P. albidus from Tahiti, Samoa, Papua New Guinea, New Caledonia, and the Philippines, and identified all of those as distinct species.²⁶

Ethnobotany

Pipturus species are used throughout the genus’ entire habitat (Table 2).^30-103

Chemical, Pharmacological, and Toxicological Investigations

Despite the abundance of ethnobotanical records, phytochemical and pharmacological investigations of Pipturus species are scarce and primarily focused on three species: P. arborescens, P. argenteus, and P. albidus.

1. arborescens

Pipturus arborescens is native to China, Taiwan, Japan, Borneo, and the Philippines. In phytochemical studies, dichloromethane extracts of the twigs yielded ursolic acid, oleanolic acid, friedelin, b-sitosterol, and stigmasterol, and extracts of the leaves were found to contain b-sitosterol, stigmasterol, squalene, and polyprenol.¹⁰⁴ These compounds may contribute to the cytotoxic effects observed in studies of various human cancer cell lines.¹⁰⁵

In another laboratory study, crude methanolic extracts of P. arborescens leaves yielded the triterpenes glutinone, friedelin, and glutinol. Further, three sterols were identified (campesterol, stigmasterol, and sitosterol). Glutinone exhibited significant antibacterial activity against Pseudomonas aeruginosa and a weaker activity against Staphylococcus aureus and Escherichia coli. Friedelin and glutinol showed no antibacterial activity against S. aureus, E. coli, and P. aeruginosa.¹⁰⁶

1. argenteus

Ethanolic and methanolic extracts of the inner bark of P. argenteus displayed selective activity against breast cancer cell line MCF-7 and have been shown to be effective butyrylcholinesterase and acetylcholinesterase inhibitors (> 80%) and possible NMDA receptor antagonists.¹⁰³

Nick et al (1995) conducted a preliminary screening for antimicrobial activity against E. coli, Bacillus subtilis, Micrococcus luteus, and Penicillium oxalicum and molluscicidal activity against Biomphalaria glabrata, as well as a brine shrimp toxicity assay. A methanolic extract of P. argenteus showed no activity/toxicity in any of the assays, except for inhibition of tyrosine-specific protein kinase of epidermal growth factor receptor (41% at 50 µg/mL).¹⁰⁷

Researchers have also investigated the antioxidant activity of P. argenteus. Scientists have reported radical scavenging activity of a P. argenteus root extract (73.7% inhibition at 14 µg/mL) and bark extract (84.2% inhibition at 35 µg/mL) using a DPPH (2,2-diphenyl-1-picrylhydrazyl) assay.¹⁰⁸ Antioxidant activity also was shown for various P. argenteus leaf and bark extracts (ethanolic, ethyl acetate, and hexane) in DPPH, ferric reducing ability of plasma (FRAP), and total phenolic content (TPC) assays.¹⁰⁹

Two patent filings in Japan suggest that P. argenteus is or was being considered as a potential skin care ingredient based on its reported active oxygen-scavenging action (for skin aging products) and/or its inhibition of hyaluronidase activity and melamine production (for skin pigmentation products). However, the former patent has expired, and the latter either has been refused or is still pending.^110,111

1. albidus

An investigation of the presence of alkaloids in 71 samples of Hawaiian plants, including P. albidus, showed no precipitates in either hydrochloric acid or ammonium hydroxide.¹¹²

Three phenolic acids ((+)-catechin, chlorogenic acid, and rutin) with antioxidant activity have been isolated from P. albidus leaves. The total antioxidant activity of P. albidus leaves, however, was found to be relatively low compared to green and black teas (Camellia sinensis, Theaceae).^113,114

The same authors investigated the nutrient and mineral composition of dried P. albidus leaves. Results are summarized in Table 3. The comparatively high calcium content in māmaki infusions is noteworthy.¹¹⁵

Another study identified eight phenolic compounds in māmaki infusions, with three caffeoylquinic acids and two flavonol glycosides being the major compounds. In the phenolic fractions, chlorogenic acid and its isomers and rutin, but not (+)-catechin, were found.¹¹⁶

Acetonitrile, methanolic, and aqueous extracts of P. albidus bark, leaf, and stem have shown antiviral activities against herpes simplex virus 1 and 2, vesicular stomatitis virus, and human immunodeficiency virus type 1 (HIV-1); antimicrobial activity against S. aureusand Streptococcus pyogenes; antifungal activity against Microsporum canis, Trichophyton rubrum, and Epidermophyton floccosum; and anti-complement activities.^117,118

Another study investigated māmaki’s antioxidant, chemopreventive, and anticancer activities. In the FRAP assay, māmaki tea exhibited a value of 40 µM/µg Trolox equivalent. Tea samples also were assessed for inhibitory activity against nitric oxide production, NF-kB activation, and proliferation of two cancer cell lines. NF-kB inhibition ranged between 60% and 75% among samples tested. Nitric oxide inhibition ranged just below 60%. Most samples were largely inactive in the cancer cell lines (> 80% survival at 20 µg/mL); only treatment with an ethanolic extract from dehydrated leaves resulted in a survival rate of 71.3%.¹¹⁹

A patent filing in Germany, Israel, and the United States suggests the use of P. albidus in a formula for hair and scalp treatment; the application is pending.¹²⁰

Commercialization and Regulatory Status

Product overview

More than 20 brands of dried māmaki tea are sold in Hawai'i through retail grocery and natural grocery stores, specialty hospitality stores, farmers markets, and e-commerce (Table 4). Most of these products are flavored with mint (Mentha spp., Lamiaceae), lemongrass (Cymbopogon citratus, Poaceae), cacao (Theobroma cacao, Malvaceae), or other local flavorings, but about one third of the dried tea (by volume) is sold as unflavored pure māmaki. The māmaki industry has gained a notable foothold within the last seven years or so.

Ready-to-drink bottled māmaki tea (e.g., Shaka Tea) is by far the dominant product type currently sold. Retail sales of Shaka Tea, which recently was acquired by King’s Hawaiian (Torrance, California), are expected to surpass $10 million in 2022. Shaka’s processing facility in Hilo, Hawai'i, receives fresh māmaki leaves from more than 20 suppliers, the largest being Ancient Valley Growers and Hawaii Forest Farms. Intake volume at the Hilo facility is close to 1,000 pounds per week, which results in about 200 pounds of dried māmaki leaf for brewing and bottling per week (personal communication with Grant Ferrier).

Cultivation Efforts

Until the early 2000s, māmaki and some other Hawaiian botanical resources were sourced largely from wild collection. A 2003 US Department of Agriculture (USDA) small business research grant supported the development of an organic Hawaiian herbal tea industry on a 25-acre experimental māmaki farm (Māmaki Farm Research). The farm, located near Hilo and owned by Kini Po-Po Creations, Inc. (Hilo, Hawai'i), resulted in full commercialization of certified organic māmaki from cultivation by 2006.¹³⁸ More recently, both academic research¹³⁹ and issuance of USDA Sustainable Agriculture Research and Education (SARE) small business grants¹⁴⁰ reflect a growing interest in overcoming limitations in māmaki cultivation. To the present day, cultivation of māmaki has experienced steady growth. Conventional cultivation still prevails. The USDA Organic Integrity Database currently lists seven National Organic Program (NOP)-certified farming enterprises growing māmaki in Hawai'i.¹⁴¹

International Market Access

A highly heterogeneous international regulatory landscape governs market access for botanical ingredients and products. While regulatory categories (e.g., for foods, supplements, medicines, and cosmetics) may appear similar, the intricacies of compliance, based on national laws, can vary widely and generally are determined by the intended use.¹⁴⁴ Market access for food ingredients may be comparatively simple, provided the ingredient is a (traditional) food and no specific health claims (other than nutritional benefits) are made. The more far-reaching the claim, the more onerous regulatory compliance becomes. Certain health benefits can be achieved outside the treatment category through unsupervised self-medication. Such products may consequently fit into the supplement category, whereas claims associated with the treatment of serious diseases typically belong to the drug category. It is important to understand these regulations and their requirements because regulatory barriers can be forbidding, and compliance may be a lengthy and costly process. On the other hand, while regulations provide a safe framework to operate within, with a sufficient degree of understanding they also hold opportunity.

Having been present in the United States as both a food ingredient and a traditional medicine, there are no obvious limitations for marketing māmaki in food and dietary supplement categories, as it is clearly “grandfathered” in both. Any structure-function claims associated with its use in dietary supplements, however, would need to be substantiated with sufficient traditional use and/or clinical evidence.

By comparison, introducing māmaki in the EU/United Kingdom would be considerably more complicated due to its historical absence in these markets. In the food and food supplement categories, it would be considered as novel food and require notification to and assessment by competent health and regulatory authorities.¹⁴⁵ As a medicine that lacks traditional use evidence from within the EU/UK, it could be marketed only as a botanical drug, which would require full market authorization — an unlikely status, given the limited data corroborating its reported activities.^146,147

Conclusion

Māmaki is an underused botanical ingredient with substantial market potential, both in terms of prospective health and nutritional benefits (based on its traditional use) and a supply chain that is relatively easy to scale up. However, the genus is poorly documented, and a taxonomic review to enable more accurate species differentiation is needed, as is further scientific exploration of the chemistry and pharmacology of Pipturus species to corroborate traditional uses. Evidence from traditional use and recent commercialization efforts demonstrates māmaki’s safe use in water infusions (teas) and ready-to-drink preparations with a tonifying effect.

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