Orites acicularis

Flowers

Immature fruit

Orites acicularis is a yellow-green coloured, woody, rounded shrub growing to approximately 1–1.5 m (3.28–4.92 ft) in height and 0.5–1 m (1.64–3.28 ft) in width, with many ascending branches.[2]

The leaves are of a conspicuous yellow-green colour; they are glabrous, sclerophyllous, approximately 10-35mm long, and rounded.[3] They taper to a sharp point, which is typically more yellow than the rest of the leaf. The adaxial surface of the leaf has a shallow central groove,[4] and the leaf margins are entire. Leaves attach to the woody stem by a 2–5 mm petiole.[3]

Flowering occurs in December, and presents upon a rachis which can be terminal or axillary. The perianth is homochlamydeous; it comprises four white-cream tepals with a groove running along the centre, and curling under to display the pink style.[3] The immature fruit is a green similar to that of the leaves. The fruits are glabrous and oblong, with a elongated tip of reddish brown. When mature, the follicle is lignified and erect, approximately 15 mm long, and boat-shaped.[3] The boat shape is due to the seeds having been released immediately upon maturity.[2][3]

O. acicularis in sub-alpine plateau habitat on Mount Wellington, Tasmania

Distribution map for Tasmania

Orites acicularis commonly occurs in Tasmanian sub-alpine mountain plateaus, heaths, and boulder fields with a geology of dolerite, granite, and diorite.[3] Dolerite's slow rate of erosion results in shallow, low-nutrient soils with an abundance of rock fragments. In sub-alpine plateaus, depressions form in the boulder fields. There, vegetable and mineral matter accumulate, creating bogs or smaller areas of deep soil. Similarly, bolster heath impedes drainage, creating shallow peats.[5]

Other species of plants that commonly grow in this habitat include: Gleichenia alpina, Astelia alpina, Baeckea gunniana, Bauera rubioides, Orites revoluta, Richea sprengelioides, Tasmannia lanceolata, and Eucalyptus coccifera.

Transverse section of leaf showing Orites-type abaxial pseudohypodermis (stained blue)

Transverse section of leaf showing the bundle sheath extension

Orites acicularis has evolved a number of characteristics to assist with protection from solar radiation in excess of its photosynthetic requirements. Two such adaptations are its abaxial pseudohypodermis and its bundle sheath extensions.[6]

Bundle sheath extensions are formed when sclerenchyma and/or collenchyma cells around a bundle sheath extend to both the adaxial and abaxial epidermis layers of a leaf.[7] The evolution of these bundle sheath extensions in species restricted to open vegetation in the family Proteaceae suggests that it is a recurring adaptation to provide protection against the high levels of solar radiation present.[6] The Orites-type abaxial pseudohypodermis is defined as multiseriate, elongate sclerids forming a reticulum around the sub-stomatal cavities (Jordan et al. 2005) and acts as a further barrier to solar radiation that lies just below the cuticle of the plant.[6]

The specific epithet, acicularis, is derived from Latin and means "needle-shaped".[8]