Among Filtered Canopies an Epiphyte Hides: Astelia solandri
- elainahanzel
- Jun 5
- 6 min read
Languorously perched among trunks and branches, a community of plants threads through the forest canopy, both emerging from and generating ecological niches in an ethereal aerial ecosystem.
As epiphytes, these heavenly bodies grow comensally, benefitting from an association with a phorophyte, supporting plant host, without harming it. Distributed vertically, they access light and derive moisture and nutrients from the atmosphere and canopy soils through specialised morphological adaptations. The humus-rich arboreal soils in which these draped and canting flora grow is composed entirely of the decomposed leaf litter and exfoliated bark of the trees on which they perch, and of the epiphytes themselves. Native host trees can similarly develop adventitious roots in response to these pocketed soils, accessing more nutrients and developing greater resilience, particularly during periods of drought, than terrestrial species.
In New Zealand, 58 vascular plant species, those with conductive xylem and phloem tissue, are considered typical or habitual epiphytes, observing an entire life cycle above ground. As such, they dominate epiphytic plant associations. These include orchids, ferns, herbs, and shrubs.
Occasional species (19) ordinarily grow terrestrially but may occasionally grow as epiphytes in trees or tree ferns and, once established, can grow to maturity. Conversely, ephemeral epiphytes (20) are often seedlings of trees or shrubs that establish as epiphytes but die before reaching maturity, as limited by resource availability or access. Hemi-epiphytes (11), taproot epiphytes, are trees that establish on other trees, tree ferns, or shrubs and then grow a taproot toward earthly soils, eventually enabling the species to grow independent of its original host, often evidenced by an irregular form- e.g. northern rātā (Metrosideros robusta).
Observed in both humid upland regions and exposed marginal forest, the geographical distribution of a species is associated with climate; distribution within the forest and forest type; exposure to wind and solar radiation; and the bark properties determining surface adherence. Densely shaded podocarp forests contain the greatest diversity of epiphytes, their reduced light and high-moisture conditions the most conducive for these vulnerable and dependent plants. Damp and protective rimu-dominant forests contain most, if not all, typical epiphytes. Largely generalists, there are no exclusive plant associations among the treetops, but the strongly horizontal branch systems of rimu (Dacrydium cupressinum) and hīnau (Elaeocarpus dentatus) accommodate the most epiphytes of all native trees. The more open and circulating canopies of beech, pōhutukawa, or rātā-tawa forests exhibit the least diversity, referring to the environmental conditions that limit epiphytic growth. Stands of Leptospermum have similarly low populations, although species diversity improves as more small trees and tree ferns arise, often aligned with increasing piripiri, filmy fern (Hymenophyllum sanguinolentum), and taupeka, comb fern (Notogrammitis heterophylla).
Epiphytic plant succession, the gradual and directional process in which community dynamics develop over time, originates with pioneering non-vascular lichens, bryophytes (mosses), and liverworts, which absorb water directly through simple leaves or cortices (moss and lichen, respectively). As these layer and accumulate moisture and organic matter, they facilitate a dampening microenvironment wherein more drought tolerant filmy ferns and orchids arise. Once established, further population and species diversity increase.
As desiccation greatly disadvantages epiphytes, adaptations to collect and conserve water are fundamental to their habit. Morphologies therefore include epiphytes with either no special means of protection against evaporation, protected epigeal parts (stems, leaves), or specialized adaptations for absorbing and retaining water. Reduced roots systems and limited soil resources influence the channeling forms of nest epiphytes which retain water and humus at the base of the plant, encouraging rootlets to ramify into the substrate. Trichomes, layered hair-like epidermal growth, regulate leaf radiation and water absorption by directly absorbing moisture and nutrients and preventing evaporation. Orchids, such as native Earina, possess velamen roots layered in a loose sheath of perforated dead cells that quickly absorb rain and atmospheric water. Further adaptations may include succulence or specialised CAM photosynthesis.
Community dynamics are also influenced by vertical microclimates, such that epiphytic strata distribution is in response to light and moisture gradients. Sciophytic (shade-loving) species, often distinguished by a deficient cuticle, are sequestered to lower positions along the trunk, where still air maintains greater ambient moisture. Filmy ferns Tmesipteris tannensis, Loxogramme dictyopteris, and Blechnum nigrum typically inhabit these shadowed niches. Heliophilic (sun-loving) species are present through the upper canopy and in lower stations exposed to columns of light. They exhibit pronounced xeromorphic features such as a thickened cuticle and water storage tissues. Epiphytic heliophiles include orchids, Pyrrosia, and Astelia.
Aloft on yawning boughs, Astelia solandri cascades over a rising system of trunks and forking branches, an immense orb and center of life and arboreal biodiversity in this complex aerial kingdom.
An endemic perennial herb, kōwharawhara or perching lily is regarded as a nest epiphyte with ensiform (sword-shaped) leaves that guide rainwater toward its center. The foliage emerges from a densely tufted basal rosette, each narrow sheath arched and drooping (100-200cm long). A monocot, its linear fronds exhibit parallel venation with three less prominent striations recognisable on either side of the midrib. The singular spring green fronds are covered in fine felt scales giving the barest pearlescent effect on the undersides of leaves, though less obviously when mature. In sun, this Astelia may also blush a slightly reddish hue.
Referred to as tākahakaha while in flower, A. solandri displays sprightly and deeply fragranced panicles of tightly clustered flowers, similar in appearance to Cordyline, through October-June. Dioecious, the female flowers range viridescent to pink, but male plants exhibit most alluring mauve flowers.
The inflorescence is 15-40cm long and emerges energetically from a 30-100cm peduncle (stalk). Small translucent green-ochre spherical berries, 4-5mm in diameter, develop between January and December. The shining and concealed globose seeds are less than 2mm long. Sweet and fleshy fruit is dispersed by frugivory, particularly among tūi, kererū, kākāriki, kākā and kōkako, endemic birds similarly attracted to the flowers' nectar.
Kōwharawhara inhabits humid coastal and lowland forests from sea level to montane altitudes in Te Ika a Māui (North Island), the west coast of Te Waipounamu (South Island), and Rakiura (Stewart Islands). These regions experience humid summers and mild, moist winters with only light frost. It can tolerate occasional, short-lived temperatures down to between -5 and -10°c, perhaps even lower if given shelter from cold drying winds. As epiphytic adaptations are associated with rupsetral growth, Astelia solandri can also be found growing terrestrially and as a lithophyte on shaded rock surfaces.
Though the substantial clusters seem unlikely and precariously perched, strong thick roots proceed from a short thickened stem and grasp the tree bark, anchoring the plant in the niches of extending limbs. Colonies often then arise and encircle the trunk. Where attached vertically to a trunk, the stem will angle upward and outward, leaning into the elements.
Its sculptural form provides essential arboreal habitat and resources for diverse specialised native birds, invertebrates, and arboreal lizards, including Moko kākāriki, Wellington green gecko (Naultinus punctatus); Mokopirirakau, arboreal gecko (Mokopirirakau granulatus); and the Pacific gecko (Dactylocnemis pacificus). Kārearea, the New Zealand falcon, does not build its own nest and may use Astelia in the canopies of emergent forest trees as high nesting platforms. The perching lily provides similar nesting habitats for ruru, morepork owls. The fountain at the base of its leaves further sustain birds, bats, reptiles, and insects during dry periods.
Its reservoir of water and detritus generates a micro-ecosystem that also develops close associations with shrubby epiphytes Griselinia lucida and Pittosporum cornifolium, which send feeder roots into the developing soils layered within the Astelia. Hanging clubmoss (Phlegmariurus varius), Hanging spleenwort (Asplenium flaccidum), and sickle spleenwort (A. polyodon) are often found draped from perching lily and similar nest epiphyte Astelia hastata, formerly Collospermum hastata (tank lily, widow maker).
Something like a keystone species, Astelia are indicative of established life in the canopy, inviting vertical complexity, resilience, and biodiversity to native forest ecosystems. It and other epiphytes are largely unseen, and under-observed, but integral to flora-fauna interactions, soil health, pollination, climate regulation, and water and nutrient cycling.
Although Astelia solandri is individually robust and long-lived, epiphytes are exceptionally vulnerable to climate change (temperature, water availability, etc), and deforestation. Small variations in humidity can disproportionately affect species distribution, with few able to acclimate to drier conditions.
Bush fragments, common remnant forest isolations in New Zealand's largely agricultural matrix, are too small to retain adequate moisture for epiphytic growth. And young, small trees inadequate for canopy communities. As the last plants to colonise a forest, epiphytes require 100 years to reestablish, 50 years beyond trees. More beneficial than planting new trees, conservation of old-growth forest is critical to protecting these sublime species and irreplaceable micro-ecosystems.
