April in the hills with Chris Horne and Michele Dickson
Muehlenbeckia astonii, pōhuehue, shrubby pōhuehue
Origin of the names
Muehlenbeckia is named after the Alsatian physician and botanist, Heinrich Gustav Muehlenbeck (1798-1845); astonii honours the work of Bernard Cracroft Aston CBE, (1871-1951), a chemist at the Dept. of Agriculture and a plant collector. His grave is in Karori Cemetery. In Te Reo Māori the name pōhuehoe is applied to several species of climbing or trailing plants. The February and March issues of In the Hills included descriptions of two other species of Muehlenbeckia, both vines, also called pōhuehue, although this month’s species is a shrub.
Distribution and habitat
Shrubby pōhuehue is endemic to New Zealand, i.e. it occurs nowhere else in the world. Its Conservation Status is ‘Nationally Endangered’. On Te Ika a Māui/North Island it occurs in scattered localities in the Wairarapa, and on Wellington’s south coast. On Te Waipounamu/South Island it occurs on coastal and other lowland sites in Westland, in Marlborough, and on Canterbury’s eastern riverbeds and terraces.
Shrubby pōhuehue can grow to 2 m tall, with a canopy up to 2 m diameter. Its growth habit is divaricate, meaning that it has numerous stems. These are up to 1 cm diameter, stiff, spread at wide angles, intertangled, and bearing many slender, flexible, interlacing, zigzag branchlets. The bark of older branches is dark grey-brown. Cane-like shoots sometimes develop from near the shrub’s base. The leaves, which grow in clusters of two or three, are 3-10 mm in diameter. They are thin, usually without teeth, heart-shaped, with the notch at the base, or with the notch at the tip. They grow on short petioles/stalks distributed along elongated branchlets. The species is deciduous, i.e. it loses its leaves in winter.
Shrubby pōhuehue is dioecious, meaning that female flowers and male flowers grow on separate plants. The flowers are minute, on very short stalks and in small bunches. The wind, and nectar-seeking birds, geckos and skinks move pollen from male flowers to female flowers to fertilise them. The clusters of tiny flowers, less than 1 cm in diameter, are greenish to white or pinkish white. The species flowers and fruits from December to February. The small seeds are black, dull, not shiny, three-sided, and enclosed by persistent sepals which sometimes become white and fleshy. Birds spread the seeds. When a camp fire on Wellington’s south coast swept up a slope including several shrubby pōhuehue, some plants recovered thanks to the presence of a lignotuber. This is a rounded woody growth on the root crown which has evolved in some species growing in areas subject to fire or drought. It contains food reserves and a mass of buds which can sprout after a fire to produce new stems.
In 1868, Colenso reported that the small, swollen, sweet, juicy, female flowers of some species of Muehlenbeckia were a popular food with Māori children. Shrubby pōhuehue is popular as a garden plant. See it at Otari-Wilton’s Bush, also on the median strip on Jervois Quay below the City-to-Sea Bridge. It is planted in numerous places in Lower Hutt, including on Petone Foreshore, the Dowse Interchange and near Percy Scenic Reserve’s car park.
Where to find shrubby pōhuehue
Look for it on the Wairarapa’s east coast, coastal fringes of the Remutaka Range, and the margins of Wairarapa Moana, Lake Onoke and Parangarahu/Pencarrow Lakes (Druce, A. P. Plant list 134). Also look for it on Wellington’s south coast. Please photograph and give the authors the grid reference, number and condition of any plants you find.
Reasons are being sought for the lack of ‘seedling recruitment’ of shrubby pōhuehue. Is the reason related to climate change, failure of the species to flower, seed predation by rodents, or paucity of pollenators?