Plate 9 Cyathea dealbata (ponga or silver tree fern)

One of New Zealand's best-known plants, with a leaflet that is the national emblem for sporting teams and the armed forces, the silver tree fern occurs in lowland to montane forest throughout New Zealand, including the Chatham Islands. It is also found on Lord Howe Island. The trunks, clothed with the persistent bases of leaf stalks, reach up to ten metres high. The name "silver fern" derives from the silvery-white colour of the undersurfaces of the leaflets, which are bright green above (and green underneath on very young plants). The rows of reddish-brown hemispherical objects between the margin and midrib on the underside of each leaf segment, shown near the top of the plate, are known as indusia. Each encloses a mass of sporangia, and each sporangium releases a mass of spores when the indusium withers under dry conditions. In the enlarged, uncoloured drawing at lower right, sporangia are shown covered (left) by two indusia and, at right, after they have withered. The enlarged drawing at left shows these same features at a lower magnification. A portion of the entire leaf (frond) is shown in the coloured part of the illustration, which is from Atlas Botanique of Voyage de I'Astrolabe (1826-1829). It was drawn by Vauthier and engraved by M. Mougeot, who also did some engravings for the botanical Atlas of d'Urville's last voyage.

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