Author: Min Geraets | BNatMed | Naturopath & Medical Herbalist
Originally published in the Avena journal of the New Zealand Association of Medical Herbalists (NZAMH).
Many New Zealand native plants remain underrepresented in contemporary herbal literature, despite a vast history of medicinal use by Māori. Kūmerahou (Pomaderris kumerahou) is one such plant and warrants deeper clinical and phytochemical consideration.
Traditionally recognised as a powerful respiratory tonic and cleansing herb, it has played an important role in Māori healing practices and early settler herbalism. Its ability to thrive in harsh environments mirror its traditional role as a restorative plant, supporting systems of elimination, respiration and inflammation. With increasing scientific exploration into its constituent profile, Kūmerahou represents a compelling example of how indigenous medicinal knowledge continues to inform modern herbal practice. Later in the article we explore what it's like to grow Kūmerahou in New Zealand with Stefany Soderling and Sam Williams, one of Phytomed's herb suppliers.
Habitat
Kūmerahou is an evergreen shrub endemic to the North Island of New Zealand. It has been found growing from Cape Reinga to the south of the Kawhia Harbour and Te Kuiti in the west, and to the northern Bay of Plenty in the east. Typically reaching no more than four metres in height, it has dark green, blunt-tipped leaves with prominent veins on the brown underside. Its pale to golden yellow flowers form dense clusters and develop into small, dry fruit.1 Kūmerahou thrives in full sun and prefers nutrient poor soil, conditions that see it commonly growing along roadside banks, in low coastal areas and gum lands, steep clay cliffs, and forest margins. Its resilience in barren and inhospitable environments gave rise to one of its European names, 'poverty weed'. The Pomaderris genus belongs to the Buckthorn family, Rhamnaceae, which includes the familiar Ziziyphus jujube.2
History
The name Pomaderris means 'membranous lid', referring to the seed covering characteristic of members of this genus.2 Known in te reo Māori as Kūmerahou, a name believed to derive from its role in traditional kūmara planting rituals. The appearance of its bright-yellow flowers signalled the optimal time for Māori to plant kūmara.3 Kūmerahou typically flowers in early spring (September - October), after which it returns to a less conspicuous state, characterised by velvety green leaves.2 Kūmerahou leaves possess a distinct bitterness, which led to their use by Māori in paikaka (fermented homebrew). Pākehā settlers also adopted this practice, using the leaves as a substitute for Hops (Humulus lupulus) in homebrewed beer.3
Saponins from Kūmerahou flowers are natural surfactants that produce a foamy lather, capable of gently cleansing the skin without stripping its natural oils. This quality awarded Kūmerahou the English name 'gum-diggers soap' among 19th-century bushmen. They discovered that rubbing the flowers with water created an effective lather for removing resinous Kauri gum from their skin.2
From a doctrine of signatures perspective, Kūmerahou flowers are akin to the alveolar sacs of the lungs. This visual likeness reinforces the herb's longstanding association with respiratory healing.
Traditional uses
Kūmerahou has a longstanding use within Rongoā Māori, particularly for conditions affecting the lungs and chest. Its therapeutic applications extend to both internal and external treatments, reflecting its versatility as a traditional medicine.
Traditionally, Kūmerahou leaves were boiled, and the resulting liquid used as a wash to soothe and heal cuts and wounds. Fresh, uncooked leaves were often placed directly onto the skin as a poultice. While leaves soaked in water were applied directly to wounds and skin irritations to sped up the healing process. Bathing in water infused with Kūmerahou leaves was a common remedy for skin irritations, sores and rashes, which was especially favoured for small children.2,3
Internally, the leaves were prepared as an infusion and taken as a general tonic. Kūmerahou was regarded as particularly beneficial for respiratory complaints, including bronchitis, asthma and tuberculosis.3 Gum-diggers were known to use the leaves as a throat gargle to relieve coughs and colds.2
Beyond its use for respiratory health, Kūmerahou was traditionally indicated for a range of conditions. These included rheumatism and arthritis, digestive concerns such as constipation, and nervous debility, where it was used as a sedative. It was also valued as a kidney tonic, blood purifier and a remedy for urinary and bladder complaints, as well as heartburn.3
Constituents
While published phytochemical data on Kūmerahou is limited; early phytochemical studies revealed Kūmerahou to contain flavonoids, including quercetin and kaempferol. Tannins, including ellagic acid and its O-methyl esters, are also present.4
Kūmerahou's significant saponin content is evident in the plant's ability to produce foam when agitated with water, a characteristic historically used for washing.3
Pharmacological actions
Traditional use and known constituents inform the pharmacological actions of Kūmerahou. It is revered for its potent expectorant properties, with saponins contributing to its effectiveness as a bronchial agent by thinning mucus and facilitating its removal from the respiratory tract.2 Saponins also provide an emollient effect when applied topically, producing a soothing and protective effect on the skin.
Kūmerahou has long been recognised for its depurative properties, traditionally valued for 'blood purifying' effects and as a kidney tonic.3 Kūmerahou's antimicrobial activity is mechanistically plausible due to its tannin content. Tannins exert antimicrobial effects by inhibiting biofilm formation and quorum sensing among pathogenic bacteria.5
Kūmerahou's flavonoid content supports anti-inflammatory effects, offering benefits for rheumatic conditions. Quercetin, has clinical evidence supporting its use as an anti-rheumatic by inhibiting granulation tissue formation in arthritis.5 Emerging research also suggests quercetin may exhibit antiviral activity by blocking early stages of viral infection and reducing associated inflammation.6
While it is widely known for its affinity for the respiratory system, Kūmerahou is gaining attention for its potential anti-diabetic effects. Emerging research has revealed the benefits of its constituent profile for diabetes management, including flavonoids quercetin and kaempferol, saponins, ellagic acid, leucocyanidin and leucodelphinidin derivatives. Although clinical studies are yet to confirm anti-diabetic efficacy in humans, these constituents are associated with mechanisms relevant to glucose metabolism and insulin sensitivity.4
Among the flavonoids present, quercetin has been shown in animal and in vitro studies to activate AMP-activated protein kinase (AMPK) and stimulate the synthesis and translocation of GLUT-4 glucose transporters, enhancing glucose uptake in cells, a mechanism similar to metformin. Additionally, quercetin appears to reduce lipid peroxidation, inhibit pro-inflammatory signalling (including NK-κB and TNF-α) and reduce oxidative stress, all of which are implicated in insulin resistance. Kaempferol, another flavonoid in Kūmerahou, has demonstrated anti-diabetic activity in animal models, restoring hexokinase activity in the liver and skeletal muscle, reducing gluconeogenesis and attenuating inflammatory responses that impair insulin signalling.4
Kūmerahou contains saponins that are associated with anti-diabetic potential. Saponins have exhibited hypoglycaemic effects in animal studies and have been shown to upregulate protein expressions of IRS-1, GLUT-4, p-AKT and p-AMPK, while down regulating pro-inflammatory cytokines and gluconeogenic enzymes, suggesting improved insulin sensitivity and glucose uptake.
Ellagic acid has been shown to decrease blood glucose and pro-inflammatory cytokines in animal models, activating insulin signalling pathways by increasing phosphorylated AKT in the liver. Although less studied, leucocyanidin and leucodelphinidin derivatives have demonstrated hypoglycaemic activity in early in vivo studies with other plant sources, indicating they may contribute to glucose-lowering effects. These constituents exert their anti-diabetic effects via multiple mechanisms, including enhanced glucose uptake, improved insulin signalling, attenuation of inflammation and oxidative stress and modulation of glucose-metabolising enzymes.4
Clinical indications
In clinical practice, Kūmerahou is mostly employed for acute and chronic respiratory conditions, including productive coughs, bronchitis and post-viral congestion. Its high saponin content produces an expectorant effect by reducing mucus viscosity and promoting its clearance from the respiratory tract.2 This makes it particularly useful when congestion is thick, sticky or difficult to expel.
Kūmerahou should also be considered in cases of low-grade inflammation, including rheumatic pain or arthritic conditions, where its flavonoid content offers anti-inflammatory and antioxidant support.5 Kūmerahou has additional benefit in a depurative protocol, supporting renal elimination in presentations characterised by sluggish detoxification and skin eruptions.3
Emerging evidence on Kūmerahou indicate a possible role in metabolic health reflects a broader shift in herbal medicine toward addressing inflammatory drivers of insulin resistance. While clinical evidence in humans remains limited, the plants constituent profile suggests potential utility as an adjunct in metabolic support when used alongside dietary and lifestyle interventions.4
Formulation considerations
Liquid extracts remain the predominant form of Kūmerahou used in clinical practice. They allow for flexible dosing and ease of combination with other herbal extracts. Its bitter taste, however, may compromise compliance among taste-sensitive individuals. This challenge can be mitigated through dilution in water or by combining Kūmerahou with aromatic herbs to enhance palatability.
For respiratory conditions, Kūmerahou combines well with demulcent herbs such as Liquorice (Glycyrrhiza glabra) or Mullein (Verbascum thapsus) to soothe irritated mucous membranes. It may also be paired with expectorant and antimicrobial herbs, including Thyme (Thymus vulgaris) or Elecampane (Inula helenium), to enhance respiratory clearance and support the immune system.
In formulations addressing inflammatory or rheumatic conditions, Kūmerahou can be paired with anti-inflammatory and circulatory stimulants such as Kawakawa (Macropiper excelsum) and Ginger (Zingiber officinale).
For depurative indications, it can be combined with Echinacea (Echinacea spp.) or Burdock (Arctium lappa) to support elimination. Additionally, in metabolic formulations, Kūmerahou can be considered alongside herbs that support glycaemic regulation and reduce systemic inflammation, including Bitter melon (Momordica charantia) and Fenugreek (Trigonella foenum-graecum).
Herbal formula for respiratory support - 200 mL
Kūmerahou (Pomaderris kumerahou) 1:2 - 60
Mullein (Verbascum thapsus) 1:2 - 60
Elecampane (Inula helenium) 1:2 - 50
Liquorice (Glycyrrhiza glabra) 1:1 - 30
Dosage: 7.5 mL twice daily. Dilute with 30 mL water or juice.
Herbal formula for inflammation and pain - 200 mL
Kūmerahou (Pomaderris kumerahou) 1:2 - 80
Kawakawa (Macropiper excelsum) 1:2 - 110
Ginger (Zingiber officinale) 1:2 - 10
Dosage: 7.5 mL twice daily. Dilute with 30 mL water or juice.
Safety and dosing
The weekly dosage range for Kūmerahou is 20 - 40 mL. From a 1:2 herbal liquid extract, 3 - 6 mL or 1.5 - 3 g of dried leaves per day should not be exceeded.7
Kūmerahou is generally recognised as safe when used within the recommended dosage range. Exceeding dosage recommendations may cause gastrointestinal irritation, due to its saponin content. Due to lack of evidence, caution Kūmerahou in pregnancy.
Introducing a Phytomed Kūmerahou supplier
The following Q&A is a conversation with one of Phytomed's Kūmerahou suppliers, Stefany Soderling and Sam Williams from Tinopai, Northland. Their perspective provides insight on the 'why' behind their valuable work. Phytomed partners with Stef and Sam for their commitment to sustainable, culturally mindful harvesting practices that ensure the highest quality herbs without compromising New Zealand's native herbal resources.
What inspired your family to grow Kūmerahou?
"A year or two before our first harvest of Kūmerahou from the property we were both struck with the beauty of its wonderful yellow flowers which only come out for a short time in spring. I had recognition of the plant from my days taking my children into a play centre, where I would then lather up the flowers with water to make bubbles and a natural soap, teaching kids how nature provides almost everything we need to survive and live well.
Sam was also familiar with Kūmerahou and referred to it as being called the 'yucks'. This affectionate referral was due to childhood memories of anytime someone got sick and didn't want to go to school, his mother Alana (now Gran), would pull out a bottle of Kūmerahou tea, which was given the name 'yucks' because of its bitter taste and unpleasant flavour. Sometimes those tummy bugs seemed to disappear in a flash, and school looked like a good option all of a sudden. Truth be told, if anyone was actually sick, the 'yucks' would swiftly aid them back to health.
Inspiration also came from the fact that Kūmerahou obviously wants to grow here, its thriving. It is possible the seeds blew down from the forestry blocks and may have been lying dormant in the ground for a long time, and for whatever reason, it wants to grow abundantly in one corner of the property where there is an acre of thick Kūmerahou which needs thinning out because so many have self-germinated and continue to do so."
Why did you choose to specialise in native New Zealand herbs rather than more commonly cultivated medicinal plants?
"We haven't necessarily chosen to specialise in natives or non-natives, our focus was more about what crops grow here naturally and have a purpose within their existence to the land and our lives, and then consideration is given to resources that are in demand and are useful to the industries involved. Sam has been proactively regenerating the property by planting as many natives as possible and continues to do so. This is now guided by our supply and purchase relationships so that everyone benefits."
Can you share some of the family history or experiences that shaped your connection to New Zealand's native plants?
"Sam grew up on this property in Tinopai, he spent time living away but has returned to build his home and lifestyle with deep roots here. He is one of four Williams children from Alana and the late Mark Williams. There are now seven grandchildren, sons and daughters-in-law, and some recent additions to the extended family who all come and go to enjoy this slice of paradise.
Tinopai is a remote rural community on the shores of Kaipara Harbour, Northland. Mark and Alana first arrived when the forestry industry was booming 45 years ago. Mark was part of the first forestry crews out here. He built them a home right off the beach using the old man pines from the property they had purchased. Many hands made light work, friends pitched in and that home remains central to the family today.
Sam's mother Alana, who still lives in that very house realised the remoteness of accessing medical advice, plus the natural way of the Rongoā based healing approach from local Māori people, who 'opened our eyes' to the alternative way of dealing with ailments and accidents. She enrolled in the Australasian College of Herbal Studies correspondence course, participated in local healing workshops and then followed to complete her nursing, midwifery training and homeopathic diploma through the College of Natural Health and Homeopathy.
Alana's views on the natural way of life, health and healing are known and trusted by her family and has rubbed off on Sam, who has quite the green thumb. Sam and Stef reconnected just a few years ago after 20 years, and now share a real passion for growing food, flowers, natives and pretty much anything which is evident by their large crops which they share amongst their people.
With natives in particular, we have access to plants that we nurture and cultivate, that are desired for health and wellbeing purposes, so we are fortunate to be able to turn work into an income stream while learning and feeling supported along the way. A kaupapa that sits well and feels good at the end of the day."
How do you ensure that your harvesting practices are sustainable and respectful of native ecosystems?
"We remain grateful every day for the means that we have, to work in and around our property, doing something that we love that has meaning at the end of the consumer line. We care for our crops and resources, harvesting gently and in a practical way so that sustainability is met.
Simple measures ensure each plant we harvest will remain strong enough to continue to thrive and give. For example:
- With certain plants, you might adopt a rule of picking a quarter or less to allow it to recover well and ensure future harvests.
- Knowing which parts of the plant is used by the purchaser is important to reduce waste and manage time effectively.
- Understanding the unique knowledge of individual plants, such as the best time/s or months of the year to harvest.
- Considering the best time of day to pick, which is almost always in the morning, especially in summer months, before the heat of the day sets in."
Do you incorporate Rongoā Māori into your work?
"Absolutely. We do our best to ensure ethical practices which respect the traditional knowledge and Māori cultural values. It's not just about 'integration', but rather a commitment to building respectful partnerships that hold different knowledge systems.
We also commit to acknowledging the spiritual dimension of Māori worldviews by following karakia protocol, using specific chants or prayers to open a harvest session, to create sacred spaces and bring balance to the work we do."
How do you maintain quality and potency when preparing your dried herbs?
"This knowledge is partly due to our own research, some is passed on from others, and some is based on guidelines according to what manufacturers want. On a daily basis, we try to only pick in the earlier mornings before the sun gets too high. This time of day and often collecting from east facing sides of the plant where possible, is when the potency of oils in the herbs is highest.
After harvesting and during the drying processing stage, we have created a purposeful space dedicated to this mahi. Its clean and sanitary. While a lot of this is new to us and we are learning as we go, we make written anecdotal records of all parts of this, so that we can alter and improve our approach to each step along the way to make sure efficiency and sustainability are key to our work."
What is the most rewarding part about growing New Zealand native herbs?
"We both agree that the best part about it is that at the end of the day we are part of a process line that helps people. These herbs aren't easily accessible to everyone, so we see it as wasteful not to allow them to be used. What's even better is that we don't have to leave our property to do it, we get to enjoy the outdoors and talk to the trees while we're doing it."
We give special thanks to Stef and Sam for agreeing to speak with us.
Final thoughts
Kūmerahou serves as a powerful reminder of the therapeutic potential embedded with New Zealand's native flora when traditional knowledge and modern science are considered together. It is a vital resource in Rongoā Māori and modern herbalism for supporting the respiratory and immune systems. Emerging research continues to uncover its wider benefits, positioning Kūmerhaou as a promising native plant within the metabolic health space. As clinical interest in New Zealand's native plants expands, it is essential to honour the cultural integrity and uphold sustainable harvesting practices, ensuring that the healing potential of Kūmerahou remains available for generations to come.
References
- Pomderris kumeraho [Internet]. New Zealand Plant Conservation Network-Rōpū hononga Koiora Taiao ki Aotearoa. 2025. Available from: Pomaderris kumeraho • New Zealand Plant Conservation Network
- Vennel, R. The meaning of trees. New Zealand. Harper Collins Publishers; 2019.
- Riley, M. Māori healing and herbal. New Zealand. Viking Sevenseas; 1994.
- Koia, J. H., & Shepard, P. The potential of anti-diabetic rākau rongoā (Māori herbal medicine) to treat type 2 diabetes mellitus (T2DM) mate huka: A review. Frontiers in Pharmacology [Internet]. 2020;11. Available from https://doi.org/10.3389/fphar.2020.00935
- Pengelly, A. The constituents of medicinal plants (3rd ed.). Boston, MA, USA. CAB International; 2021.
- Di Petrillo, A., Orrù, G., Fais, A., & Fantini, M. C. Quercetin and its derivatives as antiviral potentials: A comprehensive review. Phytotherapy Research [Internet]. 2021;36(1):266-278. Available from: https://doi.org/10.1002/ptr.7309
- Phytomed. Kūmerahou technical sheet [Internet]. 2021.