Flora of Australia Online
Xanthorrhoea Sm., Trans. Linn. Soc. London 4: 219 (1798); from the Greek xanthos (yellow) and rhoea (flowing), in reference to the yellow resin noted in the type species.
Type: Xanthorrhoea resinosa Pers.
Stems arborescent or subterranean, woody, covered with packed leaf-bases. Leaves crowded in a terminal crown, narrowly linear, tapered, rhombic to cuneate in T.S.; margins with microscopic trichomes, rarely hairy; leaf-base broad, thickened. Inflorescence cylindrical, spike-like, on a woody scape; flowers bisexual, in spirally-arranged clusters surrounded by packed bracts. Sepals free, chartaceous or scarious. Petals free, membranous; apices exserted. Stamens exserted; filaments flattened; anthers dorsifixed, dehiscing by slits. Ovary 3-locular; ovules several per locule; style simple; stigma entire, sometimes grooved. Capsule obtuse or pointed, the hardened style base ±exserted. Seeds 1 or 2 per locule, ovate and semi-matt black, rarely ovoid and shining. n = 22 (several species counted), fide B.G.Briggs, Contr. New South Wales Natl Herb. 4: 27 (1966); G.J.Keighery, Feddes Repert. 95: 523–532 (1984).
A genus of 28 species endemic in Australia.
One species (Xanthorrhoea johnsonii ) is sometimes involved in stock poisoning in Qld.
Although A.T.Lee, Contr. New South Wales Natl Herb. 4: 35–54 (1966a) and Contr. New South Wales Natl Herb., Fl. Ser. No. 34 (1966b), discussed hybrid swarms of Xanthorrhoea , documented examples indicate that hybrids are scarce and restricted. All have been on the coastal sand dunes from Beerwah, south-eastern Qld, to Newcastle, N.S.W., in restricted ecotonal conditions. The species known to be involved are X. glauca , X. resinosa , X. fulva , X. johnsonii , and X. latifolia . Hybrids probably also occur in similar conditions elsewhere on the east coast and this is certainly indicated by specimens from coastal sand dunes in Vic. Most other plants presumed to be hybrids are probably either taxa not yet recognised or examples of the considerable variation that often occurs within Xanthorrhoea species. A number of new taxa described here have been referred to purported hybrids, e.g. X. caespitosa and X. arenaria , both as X. minor × X. australis , (Lee, 1966a, p. 54 and p. 46 respectively).
All species have contractile roots and a secondary thickening meristem, the latter character absent from the other genera of the Xanthorrhoeaceae as circumscribed here. The flowers are protandrous having a style that is short at anthesis and elongates as the anthers age.
With the exception of Xanthorrhoea thorntonii all species occur in regions receiving more than 250 mm annual rainfall, and most in regions receiving more than 500 mm.
A number of characters and terms are used here for the first time. The term packing-bracts is used for the mass of small bracts that cover the axis. These are densely packed, filling out the space between the flowers and giving the surface of the spike its distinctive appearance. There is a considerable range of shape and size of packing-bracts on every spike; only the largest and most mature are described here, since immature bracts are very variable in every species. Cluster-bracts subtend the clusters of fertile and aborted flowers. All species possess cluster-bracts though in some species they are obscure at maturity, i.e. not distinguishable from the packing-bracts (see Fig. 39G–I). The terms used for the shape of the bracts are partially as in Lee (1966a), but the range of shapes recognised is expanded and some are re-defined. The shortest and least pointed bracts are obtuse (Fig. 37M) followed by shortly acute (Fig. 37N), acute (replacing intermediate) (Fig. 37 O), triangular (replacing long-acute) (Fig. 37P), narrowly triangular (replacing long-pointed) (Fig. 37Q) to the most pointed form subulate (Fig. 37R) which tapers directly from the base to the apex without the distal enlargement evident in the other categories.
Sepals and petals are described variously as beaked (Fig. 38R), and/or with proboscis (Fig. 38S), and/or with median abaxial ridge, or recurved (Fig. 38P–Q). A beak is a continuation of the sepal or petal into a terminal appendage with a small tuft of papillose hairs. A proboscis is a small adaxial projection from the beak or apex; it is always hirsute with papillose hairs. The proboscis is variable and occurs only on some of the sepals and/or petals of some species.
Crown shape is variable but is nonetheless a distinctive feature of some species. Leaf shape in T.S.— both width and thickness— are taken at the mid-point along the length of the leaf. Leaf shape terms are from the Systematics Association chart (Taxon 11: 245–247, 1962) and are illustrated in Fig. 37A–L. Scape diameter is measured just below the spike, and spike diameter is measured at the surface of the bracts at the widest point of the spike.
The shape of the leaf-base is characteristic in some species but this part of the leaf has been insufficiently collected for reliable descriptions to be provided. Capsule shape is also sometimes characteristic, but it varies during development and must be used with caution. In this treatment the only fruiting character noted is the upward-curved capsule typical of some species.
Particularly variable characters are trunk height, leaf dimensions, and scape and spike length (occasionally also the proportion). Field observation and glasshouse experiments indicate that much of this variation is environmental.
Xanthorrhoeas can rarely be identified on one or two characters alone; usually a combination of many characters is required for critical determination. As most species occur in well-defined regions, locality of collection is often a useful aid to identification. The key below is designed especially for use in the field and with fresh material, relying in part on characters such as trunk height, ratio of length of scape to length of flowering spike, and leaf colour. When collecting xanthorrhoeas for later study these data should be recorded and kept with the specimens.
G.Bentham, Xanthorrhoea (in Juncaceae), Fl. Austral. 7: 112–117 (1878); A.T.Lee, Notes on Xanthorrhoea in Eastern Australia, Contr. New South Wales Natl Herb. 4: 35–54 (1966a); A.T.Lee, Xanthorrhoeaceae, Contr. New South Wales Natl Herb., Fl. Ser. No. 34 (1966b); A.M.Gill & F.Ingwersen, Growth of Xanthorrhoea australis R.Br. in relation to fire, J. Appl. Ecol. 13: 195–203 (1976); I.A.Staff & J.T.Waterhouse, The Biology of Arborescent Monocotyledons, with Special Reference to Australian Species, in J.S.Pate & A.J.McComb, Biol. Austral. Pl. 216–257 (1981).
Data derived from Flora of Australia Volume 46 (1986), a product of ABRS, ©Commonwealth of Australia