Phylica arborea aka Island Cape Myrtle

There is no published toxicity data for Phylica arborea. The species has not been formally evaluated by the ASPCA or major veterinary toxicology references, and authoritative botanical sources (Kew's POWO, the RHS, Wikipedia) do not flag it as poisonous. On its native oceanic islands, the woody fruits are a food source for the endemic Wilkins's Bunting, which suggests the fruit is not acutely toxic to vertebrates. Treat it as unknown: keep plant material out of reach of cats, dogs, and curious children, and contact a vet or poison control centre if ingestion occurs.

In its native sub-Antarctic oceanic habitat, Phylica arborea lives under near-constant moisture from rain, fog and cloud cover, yet always on well-drained volcanic slopes. In cultivation this translates to moderate, regular watering: keep the root zone evenly moist but never standing in water. The thick, leathery, needle-like leaves offer some tolerance to short dry spells, but prolonged drought is not natural for the species. Reduce watering noticeably in cool weather.

Phylica arborea grows naturally on volcanic oceanic-island soils — rocky slopes, plateaus and coastal outcrops over basaltic parent material, often with an organic peat-like topsoil. The best cultivated mix is light to medium textured and sharply drained: a free-draining loam amended generously with coarse grit, pumice or lava rock, plus some organic matter to hold moisture. Aim for a slightly acidic to neutral pH. Avoid heavy clay, soggy mixes and anything limey or alkaline.

Give Phylica arborea as much direct sun as you can. On Gough and Tristan it is a canopy or near-canopy plant on open, wind-exposed slopes, often with no overstory at all. Its narrow, leathery leaves with silvery-downy undersides are classic adaptations to high light and constant wind. Indoors it rarely thrives — plan on an outdoor position in full sun (in cool-summer climates) or the brightest, most open spot you can offer under glass, with good air movement.

Phylica arborea is an oceanic-island species that lives in almost perpetual humidity: the fernbush zones of Gough Island where it dominates are regularly wrapped in cloud, fog and salt-laden spray, and its branches typically carry dense growths of mosses and lichens. In cultivation it strongly prefers high ambient humidity combined with cool temperatures and steady air movement. Dry, warm indoor air is a poor fit; a cool greenhouse, mist house or sheltered maritime garden is a much better environment.

Phylica arborea is a slow-growing evergreen shrub or small tree. In its native oceanic-island habitat it can reach 6–7 m tall in sheltered gullies, with specimens up to about 7.6 m recorded, but it is typically much smaller — around 3 m tall and 2 m wide — in the open wild and only 1.5–2.5 m tall and wide in UK cultivation. The RHS puts time to ultimate height at 10–20 years, so expect a gain of only a few centimetres a year. Growth is fastest in cool, humid oceanic conditions with steady moisture and well-drained, acidic soil.

Phylica arborea is adapted to a cool, oceanic climate with remarkably little seasonal variation — its native islands sit between roughly 10 and 15 °C year round. It thrives in mild summers (ideally below about 25 °C) and cool but largely frost-free winters. The RHS rates it H2, meaning it only reliably tolerates minimums of 1–5 °C and should be overwintered in a cool greenhouse in most of the UK. European growers report it can survive brief dips to about -12 °C in sharp-draining soil, corresponding to USDA Zones 9–10. Strong cold winds are more damaging than cold itself.

Phylica arborea produces dense terminal clusters of small, greenish-white flowers with a light honey scent, typically blooming in the Southern Hemisphere spring and early summer (November to January in its native range). Individual flowers are inconspicuous, but in full flush the clusters form creamy heads at branch tips. After pollination, the plant produces small hairy capsules containing seeds that are dispersed by endemic island birds.

Phylica arborea is pollinated by insects. Its small, honey-scented, greenish-white flowers clustered at branch tips match the classic insect-pollination syndrome. On its remote oceanic islands the actual pollinators are a small set of endemic flies and other invertebrates, since bee diversity is low. Seed dispersal is distinct from pollination: fruits are eaten and dispersed mainly by endemic land birds, including the Critically Endangered Wilkins's Bunting.

The flower clusters carry a light, sweet, honey-like fragrance that is typical of many Phylica species. The scent is subtle rather than strong, matching the small size of individual blooms, and is most noticeable when several clusters are open at once. The foliage itself is not notably scented.

Phylica arborea is not a food plant. There are no culinary uses for any part of the tree, and it is not cultivated or harvested for human consumption. The small woody fruits are eaten by endemic island birds (notably the Wilkins's Bunting), but this does not make them palatable or safe for humans.

There are no documented medicinal or ethnobotanical uses for Phylica arborea. As an extremely restricted oceanic-island endemic with a very small historical human population on Tristan da Cunha, it has never entered traditional medicine. It should be regarded strictly as an ecological keystone species, not a therapeutic plant.

Phylica arborea's main importance is ecological rather than commercial: it is the sole native tree of Tristan da Cunha and Gough Island and provides nesting habitat for the Endangered Atlantic Yellow-nosed Albatross and critical food for the Critically Endangered Wilkins's Bunting. Historically, Tristan islanders used the wood for firewood and small-scale construction, since no other tree species was available. Today it is largely a conservation subject — the focus of IUCN-listed recovery programmes rather than horticultural trade.

Phylica arborea is extremely rarely cultivated outside its native South Atlantic and Indian Ocean islands, and it is considered challenging to grow. It requires a cool, frost-free maritime climate with steady moisture, high humidity, and strong light — conditions that are difficult to reproduce inland. Even specialist growers report inconsistent performance, and the species has not established itself in general horticulture.

Phylica arborea is endemic to a handful of remote oceanic islands. It grows wild on the Tristan da Cunha archipelago (including Tristan, Inaccessible and Nightingale) and Gough Island in the South Atlantic, and on Amsterdam Island in the southern Indian Ocean. On Tristan and Amsterdam it is the only native tree; on Amsterdam Island the last dense stand now survives in just ~10 hectares at Grand Bois.

In the wild, Phylica arborea grows on nutrient-poor volcanic soils enriched mostly by seabird guano and leaf litter, so it is adapted to lean conditions and does not need heavy feeding. If grown in cultivation, a light dressing of balanced slow-release fertilizer in spring is more than enough; avoid rich or high-nitrogen feeds, which can push soft growth vulnerable to wind and cold. As a Rhamnaceae relative of Cape-native Phylica species, it likely dislikes phosphorus-heavy fertilizers.

In its native range, Phylica arborea experiences cool, wet, windy maritime conditions year-round with mild winters and no extended frost. In cultivation, treat it as a cool-temperate evergreen: keep it steadily moist and airy in spring and summer, reduce watering slightly in winter, and protect it from hard frost at all times, as seeds and seedlings are particularly frost-sensitive. Avoid hot, dry summer spells by providing afternoon shade and mulch in warmer climates.

No named cultivars or horticultural varieties of Phylica arborea are recognised. Botanists do note variation between island populations, and the Amsterdam Island plants have at times been treated as the distinct form Phylica nitida, but this is generally lumped back into P. arborea. For growers, there is effectively only one form on offer, typically propagated from seed collected on Tristan or Gough.

Phylica arborea can be grown outdoors only in mild maritime climates that mimic its native Tristan da Cunha conditions, such as coastal parts of the UK, Ireland, New Zealand, southern Australia and coastal California. It needs full sun, free-draining soil, steady moisture, and shelter from cold drying winds and hard frost. It is not hardy enough for continental winters and is not suited to hot, dry inland gardens.

Phylica arborea naturally forms a dense, thicket-forming shrub or small tree and needs little pruning. Light tip-pruning after flowering can encourage a bushier habit and help it withstand wind, and any dead or wind-damaged branches can be removed at any time. Avoid heavy cuts into old wood, as Rhamnaceae species generally do not resprout reliably from bare wood.

As a woody tree that can eventually reach 6–7 m, Phylica arborea is not a long-term container plant, but young specimens in pots can be potted on every 2–3 years in spring into a slightly larger container with gritty, free-draining compost. Handle the rootball gently, as Phylica species dislike root disturbance. In the long run it is better placed in the ground in a sheltered, frost-free spot than kept pot-bound.

Phylica arborea is propagated almost exclusively from fresh seed. Conservation programmes on Amsterdam Island used seed from surviving trees to replant around 7,000 seedlings after cattle were removed, so seed is clearly viable when conditions are right. Germination is slow and patchy and is strongly suppressed by frost, so seeds should be sown fresh in a frost-free, bright propagator in gritty, free-draining compost. Semi-hardwood cuttings may work, as they do for related Cape Phylica species, but success is poorly documented.

Phylica arborea is rarely cultivated, so there is little species-specific guidance on leaf problems. As a general rule for this kind of cool-maritime evergreen, yellowing leaves most often point to waterlogged or compacted soil, poor drainage, or a lack of micronutrients on overly alkaline soil. Check that the roots are not sitting in water, ease up on fertilizer, and consider whether the plant is being pushed too hard by dry indoor heating or hot summer sun.

Because Phylica arborea is rarely grown in cultivation, brown leaves should be interpreted from general woody-evergreen principles. The most likely causes are cold or frost damage (the species is clearly frost-sensitive), dry drying winds, sunscorch in a hot climate, or drought stress. Brown, crispy leaf tips usually mean the plant is losing water faster than its roots can replace it.

There is very little specific literature on drooping in cultivated Phylica arborea, as the species is rarely grown. In a general woody-evergreen context, drooping branches usually reflect either underwatering and drought stress, or the opposite problem of saturated, airless soil that is damaging the roots. Recently repotted or transplanted specimens may also droop briefly while they re-establish.

Phylica arborea is evergreen and should normally hold its leaves year-round, so noticeable leaf drop is a sign something is wrong. Given how rarely it is cultivated, the likely causes are the same as for other cool-maritime evergreens: sudden environmental change (transplant shock, a move indoors or outdoors), cold or frost damage, drought stress, or root problems from overwatering. A light, steady loss of the oldest interior leaves is normal.

Phylica arborea is naturally a slow-growing tree in its wild island habitats, where exposed wind-blasted specimens stay stunted and even sheltered trees rarely exceed 6–7 metres. Slow growth in cultivation is therefore usually not a problem, especially in cool climates or in containers. If growth seems unreasonably poor, check for waterlogging, excessive shade, or lack of warmth during the growing season.

In the wild, the main threats to Phylica arborea are not classical pests but introduced species: cattle and livestock on Tristan and Amsterdam Island historically destroyed whole forests, and invasive house mice on Gough Island have been linked to seed predation and failed regeneration. More recently, an introduced sap-sucking brown soft scale (Coccus hesperidum) has infected 85–100% of trees in some stands on Tristan, with biocontrol using Microterys nietneri starting in 2021. Like most Rhamnaceae it can also be vulnerable to root rot in waterlogged soil.