Bark anatomy of three indigenous conifers from southern South America

Abstract

This paper describes the bark anatomy of three native conifers from southern South America, Podocarpus nubigena Lindl., Saxegothaea conspicua Lindl. (Podocarpaceae) and Araucaria araucana (Mol.) K.Koch. (Araucariaceae). The bark colours of these three conifers are greyish-brown, reddish-brown and true brown, respectively. Morphologically, the bark of S. conspicua is scaly whereas it is fissured in A. araucana and P. nubigena. Fissures are relatively shallow in P. nubigena and relatively deep in A. araucana. The latter two species have elongated stripes and polygonal to irregular plates, respectively. Anatomically, P. nubigena shows a gradual transition between non-collapsed and collapsed phloem. This species shows secondary phloem cells regularly arranged in continuous tangential bands composed of alternating sieve cells, axial parenchyma and fibres. In A. araucana the ordered pattern observed in the non-collapsed secondary phloem is lost in the collapsed phloem. All three species show homocellular and uniseriate rays exhibiting a sinuous trajectory in the collapsed phloem and into the rhytidome. Fibres in P. nubigena are arranged in narrow, tangentially uniseriate lines. Sclereids are observed in S. conspicua whereas ramified sclereids and fibres are present in A. araucana. Minute cell-wall crystals in the fibres are exhibited in all species. The persistent rhytidome occupies a variable proportion of the bark. A. araucana shows thick periderms and rhytidome, with indistinct rays in dead phloem. Starch, tannins and resins are frequent in parenchyma. Secretory canals are present only in A. araucana. In summary, the external morphology, arrangement of axial parenchyma, type of the sclerenchymatous tissue, presence of secretory canals and cell-wall crystals are the most important features that can be used for identification when other diagnostic plant parts are missing.