Sophora microphylla

Sophora microphylla is a moderate to large tree in the family Fabaceae. It reaches in height, with a trunk up to in diameter, although more commonly in diameter. The bark is smooth and greyish-brown in colour. Branches are weeping and spreading. The wood of the New Zealand Sophora is dense, very durable, tough, and is of high value. The sapwood is pale-brown and the heartwood is yellowish-brown. It is straight-grained. Sophora microphyllas young form is distinct in that it resembles a small, bushy, divaricating shrub. The branchlets are initially glabrous, but then transition to pubescent in adulthood. Young leaves are arranged alternately, and very small, growing on yellow to orange-brown interwoven twigs. The leaflets are 3.0–5.8 × 2.3–4. mm long, broadly obovate to nearly circular in character, ranging from almost hairless to lightly hairy, and spaced apart rather than crowded or overlapping. Adult leaves are up to long and generally pinnate. Leaflets on adults are 4.5–12.5 × 2.3–5.7 mm long, usually broadly elliptic to obovate, and are not crowded or overlapping. The upper surface is light green to green, and the under surface is light green. They are moderately hairy. The inflorescences (flower clusters) have up to seven flowers per cluster. The peduncles are 10–25 mm long, and the pedicels are up to 16 mm long. Flowering generally occurs from August to October, but may start in May. Flowers are drooping and bright yellow in colour. The bracts (specialised leaf structures) are 1.8–3.4 mm long. The calyxs are 5–11 × 7–10 mm long, and shaped like a cup. The corollas are yellow. The ovaries are 8–17 mm long. The styles 10–15 mm long. The anthers (pollen containing parts) are 2.0–2.5 × 1.0—1.3 mm long. Sophora microphyllas seeds are found in long, brown, pea-like pod structures. Fruiting occurs from October to May. The seed pods are 50–200 mm long, ridged, and contain up to 12 seeds. The seeds are 5.5–8.5 × 4.0–5.5 mm long, and yellowish in colour. S. microphylla has a diploid chromosome count of 18. ==Taxonomy==

Sophora microphylla was first described by the Scottish botanist William Aiton in 1789. There are 64 species of the Sophora genus currently accepted by the Plants of the World Online taxonomic database. These species are found throughout the entire world. There are three recognised synonyms of the species, Edwardsia grandiflora var. microphylla and Sophora tetraptera var. microphylla described by the botanist Joseph Dalton Hooker, and Edwardsia microphylla described by the botanist Richard Anthony Salisbury. There are eight species native to New Zealand. Sophora is a relatively recent arrival to the New Zealand flora, having diverged an estimated two million years ago. S. microphylla is categorised in section Edwardsia of the Sophora genus. S. microphylla is most closely related to toromiro (S. toromiro). The biogeographic and phylogenetic characteristics of the section Edwardsia in the Sophora genus were studied by Peña et al. (2000). Etymology The etymology (word origin) of S. microphyllas genus name, Sophora, derives from the Arabic name which refers to trees in the Fabaceae, the pea family. The specific epithet (second part of the scientific name), microphylla, means 'small leaf', and refers to the small leaves of this species compared to other members of the genus. The species is commonly known as kōwhai, weeping kōwhai, and small-leaved kōwhai. It is also referred to as the common kōwhai or the South Island kōwhai. The word 'kōwhai' comes from koofai, a word used in an ancient Polynesian language for 'pod-bearing' plants. The word 'kōwhai' is also the Māori language word for the colour yellow. ==Ecology==

Sophora microphyllas seeds are dispersed by gravity, wind, or by water. The seed pods of the Sophora genus can travel long distances in water through transoceanic dispersal. S. microphylla is pollinated by birds; the tūī (Prosthemadera novaeseelandiae) are especially attracted to the flowers and are the primary pollinator of the species. They will also travel long distances in search of it and defend the tree from other birds. Other birds, such as the New Zealand bellbird (Anthornis melanura), kākā (Nestor meridionalis), and silvereyes (Zosterops lateralis) also visit the flowers, either for nectar or pollen, as the flowers produce large amounts of nectar. The introduced birds, chaffinches (Fringilla coelebs) and house sparrows (Passer domesticus) are recorded as floral visitors, as well as butterflies and bees. The native kererū (Hemiphaga novaeseelandiae) instead eat or browse the leaves and flowers. Several beetles and caterpillars feed on the plant, including the kōwhai moth (Uresiphita polygonalis), variegated longhorn (Coptomma variegatum), and lemon tree borer (Oemona hirta). New Zealand drywood termites (Kalotermes brouni) can establish themselves inside the heartwood of the tree. S. microphylla also supports gall midges and weevils. New Zealand fantails (Rhipidura fuliginosa) can also be attracted to the tree to browse for insects that may be on it. Research by Pole (2022) suggests that the now-extinct, moa, consumed Sophora species, but were not effective at dispersing the seeds. Sophora microphylla has low to moderate flammability rates, according to a 2016 study. A nitrogen-fixating plant, S. microphyllas nodules (specialised root structures) can improve soil quality. These nodules are found on their roots. S. microphylla can be brevideciduous or semideciduous in some southern localities. The terms brevideciduous and semideciduous refer to plants that lose their leaves, either entirely for a very brief period or partially, respectively. Toxins The primary alkaloid responsible for S. microphyllas toxicity is called cytisine. Every part of S. microphylla, especially the seeds, is poisonous to humans and some other animals. Other alkaloids found in Sophora include, but is not limited to: anagyrine, diosmin, hesperidin, and matrine. There are reports of people becoming seriously ill after using cutlery made from Sophora wood or from consuming birds that had fed on the plant. Poisoning symptoms may include an increased heart rate, loss of coordination, muscle twitching, nausea, and vomiting. In severe cases, paralysis and respiratory failure may occur. The ingestion of Sophora leaves in cattle has resulted in several deaths, and the seeds have been proven to be toxic to mice and honeybees. ==Distribution==

Sophora microphylla is endemic to New Zealand. Its range mainly covers the South Island, but is also present in the North Island. It is somewhat uncommon in some parts of the North Island where it is replaced by other Sophora species. It is not found in the northern parts of Hawke's Bay or East Cape. Observations in the Northland Region and Auckland suggest that S. microphylla mainly grows inland there and may have been replaced in coastal areas by the coastal kōwhai (S. chathamica). The species also does not naturally occur on Stewart Island. Its conservation status in the New Zealand Threat Classification System was assessed in 2023 as "Not Threatened". Habitat Sophora microphylla is found in various habitats. S. microphylla typically inhabits coastal to lower montane environments, reaching above sea level at maximum elevation. S. microphylla has been described as "fast-growing" and "very wind-resistant". The plant is primarily found on alluvial river terraces, floodplains, lake edges, riparian forests, sand dunes, and hillside slopes where the ground is composed of loose, rocky debris. In these environments, it typically occurs in shrublands or within mixed podocarp and hardwood forests. A light-demanding tree, S. microphylla may be commonly associated with cabbage trees (Cordyline australis), narrow-leaved lacebarks (Hoheria angustifolia), and lancewoods (Pseudopanax sp.). ==Uses==

The vibrant, yellow, flowers of the New Zealand kōwhai (Sophora sp.) are well-known and are unofficially recognised as the national flowers of New Zealand, having been a common subject of artwork and a national symbol for the country. Despite their potential toxicity, the plants have been used by indigenous Māori people and European settlers for timber, medicine, cultivation, and in other practices. Māori used the durable, hardy timber for a wide range of purposes, including using it in the making of canoe paddles, farming tools, and weapons. Its strength made it suitable for digging sticks and weapons, while its flexibility made it useful for bird snares and eel spears. The timber was also used in building houses and for fencing. European settlers similarly valued the timber because of its properties. It was commonly used for fence posts. They also used it for railway sleepers, houses, bracing in wharf construction, furniture, cabinetry, decorative woodwork, tool handles, among other uses. The plant was also used in traditional medicinal practices. The primary medicinal use was the bark being used to create infusions that would treat sore throats. Māori also used the plants to make natural dyes. Sophora in New Zealand is commonly found in places where it may have been cultivated by Māori people and is often associated with pā (fortress) sites. ==References==

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