Pherosphaera hookeriana

Pherosphaera hookeriana
Pherosphaera hookeriana
Scientific classification
Kingdom:	Plantae
Division:	Pinophyta
Class:	Pinopsida
Order:	Pinales
Family:	Podocarpaceae
Genus:	Pherosphaera
Species:	P. hookeriana
Binomial name
Pherosphaera hookeriana W.Archer bis

Pherosphaera hookeriana is a dwarf conifer endemic to Tasmania, and grows at altitudes above 600 meters. There are roughly 30 known sites, with population numbers in the tens of thousands. The species occurs in a range of habitats typically in areas near water bodies, mostly on dolerite geology. The species is highly fire sensitive and an increase in fire events associated with climate change may lead to local extinction in some areas and fragmentation of habitat

Pherosphaera hookeriana is a densely-branched erect shrub or small tree growing to heights of 5 meters, branches are often small and rigid with leaves arranged spirally and fully appressed to the stem. Individual leaves can measure up to 1.5 millimetres (mm) long, and 1 mm wide, leaves are thick, blunt and concave with a rounded keel. Male flowers in compressed, terminal globular cones, ranging from 1-5 mm in diameter, with 8 to 15 fertile scales, each scale has two pollen sacs on the abaxial surface. Female flowers occur in cones on short branches that usually droop (hence the old common name) flowers are globular ranging from 2-4 mm long and have 3-8 fertile scales, with a single ovule on the upper surface of each scale. When the seed is ripe it has a hard, glossy brown coat and is approximately 1mm in diameter [Description from Curtis & Morris (1975), Hill (1998)]

Pherosphaera hookeriana is a dwarf conifer that has been recorded to grow up to 5 meters, but in exposed and harsh environments it may only attain a height of 0.5 meters (Minchin 1983). The foliage of Pherosphaera hookeriana is well adapted to the high altitudinal ranges it occupies, with small imbricate scale leaves, the stomata are restricted to the adaxial surface and protected by a marginal leaf frill (Hill and Brodribb 1999). The species is generally dioecious, with the reproductive organs occurring on specialised leaves arranged in cone like structures. Pollen is wind dispersed and seed ripening occurs by late April (Wood & Rudman 2015). It is unclear if the plant produces seed annually or produces mass seed every few years (mast seeding). Recruitment of seed appears to happen only rarely and is restricted to moist, shady areas. Seed is noted as having a physiological dormancy which could potentially result in a soil stored seed bank with germination being staggered over several years. It is unknown how long the seed is viable in the soil for, but preliminary studies show that the seed requires warm stratification and then cold stratification to elicit germination; so the earliest recruitment would take place is in the second spring/summer following dispersal (Wood & Rudman 2015). Seedlings superficially resemble small lycopods, with narrow spreading leaves. The seeds are not winged so it is expected to drop within a few meters of the parent plant. It has been suggested that dispersal over long distances via water is possible for plants occurring near lakes and rivers. Pherosphaera hookeriana may form extensive clonal colonies via vegetative growth (Fitzgerald 2011). Like most endemic alpine conifers to Tasmania, the growth rate of Pherosphaera hookeriana is extremely slow. Plants that have a stem diameter of 3-6cm having an estimated age of 250-300 years on Mawson Plateau (Minchin 1983) with the actual maximum ages likely exceeding 500 years. The time frame for plants to reach reproductive maturity is unknown, though there were observations of fruiting plants on the Tarn shelf in 2016 in areas that suffered fire damage in 1966. Pherosphaera hookeriana is one of only two species in the genus, and is one of the five taxa in the Podocarpaceae family with four being endemic to Tasmania (de Salas & Baker 2016)

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