The NZ Native - Kumerahou

Kūmerahou - a unique shrub from northern Aotearoa

Kūmerahou (Pomaderris kūmerahou) is a native shrub which is endemic only to the upper North Island and Coromandel. It produces creamy yellow flowers in early spring around the time that kūmara or kumera is traditionally planted. While once commonly found in poor clay soils, it has become somewhat less widespread in recent decades.
This is one of our most highly regarded medicinal native plants. It has a particularly strong reputation for its use in a few different bronchial conditions. The leaves were boiled or infused, and the liquid was taken internally for all manner of chest complaints, including bronchitis, pulmonary tuberculosis, and asthma. Bronchitis was treated with it at least as early as 1840, and it was popular as an alleged cure for coughs and colds. It was also widely used in early 1900s to treat tuberculosis. In the 1930s it became popular also in the treatment of asthma ^(1-3).

While medical herbalists now have multiple phytomedicines to choose from when formulating treatments for upper respiratory tract infections and coughs. Kūmerahou remains one of the best. It is certainly one to turn to where the patient has a stubborn or prolonged cough that has been hard to shift. It has a very bitter taste, and so sweetening it with some liquorice, hoheria, marshmallow or honey, is often recommendable.
Kūmerahou is a strong expectorant and anti-inflammatory, and so even relatively small amounts of 15-20% in a cough formulation or doses of 2-3mL as a simple, can be sufficient, though more can be used if needed. As with all expectorants though, excessive doses can trigger emesis. While it is suited best for dry coughs, it can really shift stuck mucous, and ease a bad and prolonged nocturnal cough. This is particularly when mixed with the above or other cough herbs, such as white horehound or elecampane.

Kūmerahou isn’t just a good remedy for chest conditions. There are many other traditional and modern-day applications it can be used for. Its rich content of saponins is responsible for its value as a cleansing agent and emollient. There is historical use by the kauri gum diggers, at the end of the 19^th and early 20^th centuries, as a popular soap substitute.

This led to the name ‘gum digger’s soap’ that was once given to it.One of its main traditional uses, is as with many of our native species, to heal wounds, sores, and rashes. The leaves were applied topically in a variety of manners for this purpose, and in addition to its cleansing properties it can be helpful for a wide range of rashes. Also, including eczema, psoriasis, and other inflammatory skin conditions. Such topical use can be complemented by it being given also internally for these conditions.

Related to these uses perhaps is kūmerahou reputation as a so-called blood cleanser. It was once popular for assisting with detoxification following overindulgence with alcohol and was sometimes used to settle an upset stomach and as an anti-emetic. It was also a sought-after tonic for the kidneys, and for kidney and liver weakness. Alongside, its gentle aperient action, it may facilitate increased elimination of toxins and unwanted waste products through the kidneys and liver.

Such abilities may also indirectly assist with inflammatory or rheumatic joint conditions. Kūmerahou gathered quite a reputation for helping with rheumatism amongst Māori, and European and Chinese settlers. Early Chinese settlers and healers were very adept at adapting to their new country. They were using many of the native medicinal plants that grow here, to supplement their use of traditional Chinese medicines.
Apart from saponins, kūmerahou contains quercetin and many other flavonoids, some of which are likely to contribute to these anti-inflammatory properties. These are likely to be produced through both topical and internal administration. Case reports also exist of it being useful as a galactagogue, and for uterine or menstrual pains, and for diabetes.

These, however, remain unsubstantiated. Finally, while its medicinal applications are debatable, kūmerahou leaves were also found to make a type of fermented homebrew – paikaka. Back in the day before Aotearoa New Zealand had a robust hop growing industry as now. The European settlers and missionaries were often on the lookout for innovative new alcohol recipes and found that the leaves made a good substitute for hops when brewing beer.

Unfortunately, there has been little research into this unique native plant, which has few botanically related cousins, and has a limited distribution throughout Aotearoa. As such, it is important that we find out more about it, including the impact of human development and on its future sustainability, while respecting its valuable medicinal attributes.

References:

1. Brooker SG, Cambie RC, Cooper RC. New Zealand Medicinal Plants. Heinemann Publishers, Auckland, 198

2. Riley M., “Maori Healing and Herbal: New Zealand Ethnobotanical Sourcebook”, Viking Sevenseas, Paraparaumu, N.Z., 1994.

3. Rasmussen PL, New Zealand Native plants and their clinical applications for respiratory conditions, Phytomed Seminar, June 2015.