Pennantia baylisiana, commonly known as Three Kings kaikōmako or kaikōmako manawatāwhi (Māori), is a species of plant in the family Pennantiaceae (Icacinaceae in older classifications). It is endemic to Manawatāwhi / Three Kings Islands, around 55 kilometres (34 mi) northwest of Cape Reinga, New Zealand. At the time of its discovery just one plant remained. This single tree grows on a scree slope inaccessible to browsing goats, and has been called "the world's loneliest tree". The species was discovered in 1945 by botanist Geoff Baylis and described in 1948, although it took decades before it was fully accepted as a distinct species of Pennantia. Although the only wild tree is female, it was successfully propagated from cuttings in the 1950s, one of which was induced to self-pollinate in 1985. Subsequent seed-grown plants have themselves set seeds, and the species has been replanted on the island, the adjoining mainland, and in public and private gardens around New Zealand.
Description Pennantia baylisiana is a shrubby, multi-trunked tree with a broad crown, unlike the three other species in the genus Pennantia. It does not have a divaricating juvenile form, unlike the other New Zealand Pennantia species kaikōmako (P. corymbosa). It grows to a height of 5 m in the wild, though has been recorded reaching 8 m in cultivation. It has pale greyish-brown bark and branchlets that are covered with lenticels. It has leathery, green, egg-shaped alternate leaves around 12–16 by 7–10 cm. Adult leaves have smooth margins but young leaves are toothed. The leaves are large and flat in shade-grown plants, up to 20 by 10 cm, but notably curled along their sides – almost rolled – on branchlets exposed to sun and wind. They have distinctive hair-covered domatia on the underside, at the junction of the midrib and secondary veins, and are suspended from 2.5 cm long petioles. Flowering occurs from October to November, producing 1.5 by 1.5 mm greenish-white flowers in panicles with 2.6 mm petals. Flowers usually arise on woody branches, though some are terminal. The stamen is made up of a 1–1.4 mm long anther on top of a 1.5 mm long filament, though the pollen is usually sterile. It has a 2.8 by 2 mm cylindrical ovary with a stigmatic ring 1.5–1.8 mm in diameter. Fruiting is from January through to April in cultivated plants yielding 10 by 4.5 mm ellipsoid fruit. Mature fruit are purple to black and have a single hard 9 by 3.5 mm seed. Its chromosome number is 2n = 50, as with P. corymbosa.
Discovery
Pennantia baylisiana was discovered by New Zealand botanist Geoff Baylis in 1945 when he visited Great Island, the largest of the Manawatāwhi / Three Kings Islands, on a botanical expedition. The Three Kings are located around 55 kilometres (34 mi) northwest of Cape Reinga, and at the time were relatively unknown botanically, with the only collecting expeditions in 1887 and 1889 (both by Thomas Cheeseman, director of Auckland Museum, who had only a few hours ashore), 1928, and 1934. Baylis spent a week on the island in November–December 1945, and collected samples of 83 species of plants for Auckland Museum.By this time wild goats had eaten the place out. Part was closely browsed grass but most was kanuka forest or scrub. Cheeseman's novelties survived in small numbers beyond browse range. It was easy to see that the grassland offered nothing new, but the kanuka canopy was broken here and there by other textures and shades of green. I located these places by climbing trees at every vantage point and reached them deviously via bluffs and screes since except in the main valley they were, even for goats, a bit inaccessible.Four of Baylis's discoveries were new to science, including Suttonia dentata (now Myrsine oliveri), Tecomanthe speciosa (which like P. baylisiana was represented by a single living individual), and Brachyglottis arborescens. After collecting the latter two, he describes coming across P. baylisiana:The last little grove that I investigated lay near the highest point of the island down a scree of boulders about 200m above the sea. I was drawn to it by what looked like a karaka. I was soon gazing upon it in disbelief since a third find seemed too much to expect. But this was no karaka – its leaves were larger and recurved strongly in the sun, its bunches of small green flowers sprang from the bare branches below the leaves and there were no big berries – indeed none at all.He noted that the 4.5-metre tree was living on a seaward scree slope of greywacke boulders at an altitude of 233 metres, with pōhutukawa (Meterosideros excelsa), kānuka (Kunzea ericoides), coastal maire (Nestegis apetala), and whārangi (Melicope ternata) growing nearby. The tree was forked at the base and badly eaten by insects. Baylis collected the holotype specimen of P. baylisiana (housed in Auckland War Memorial Museum) on 2 December 1945.
Taxonomy The species was described by Director of Auckland Museum Walter Oliver in 1948. Oliver noted its resemblance to the genus Corynocarpus, which includes the New Zealand species karaka (Corynocarpus laevigatus). Corynocarpus had until recently been considered to be in the family Anacardiaceae, which is where Oliver placed this species, erecting a new genus Plectomirtha to contain it and giving it the specific epithet baylisiana in recognition of the plant's discoverer Geoff Baylis.
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