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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.
Blackboy, Grass-tree, Yacca.

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).

1 Scape 8 or more times as long as spike; flowering spike broad and brush-like from the very long erect filaments; stomates in linear, subsurface, hair-lined chambers (Fig. 37S)


1: Scape 5 or less times as long as spike; flowering spike ±cylindrical, the filaments short and erect or, if longer, recurved; stomates at leaf surface or if sunken, then each in a pit (Fig. 37T)


2 Packing-bracts glabrous (eastern Australia)


2: Packing-bracts hirsute (W.A.)


3 Spike longer than scape


3: Spike shorter than or equal to scape


4 Packing-bracts subulate, glabrous


4: Packing-bracts shortly acute to triangular, glabrous to hirsute or fringed with hairs


5 Leaves 5–12 mm wide


5: Leaves 1.2–3 mm wide


6 Spike only slightly longer than scape (W.A.)


6: Spike usually much longer than scape (eastern Australia)


7 Cluster-bracts obscure or almost so


7: Cluster-bracts prominent for at least part of spike


8 Leaves 4–8 mm wide


8: Leaves usually less than 4 mm wide


9 Trunk to 60 cm long (W.A.)


9: Trunk usually 2–6 m long (N.S.W.)


10 Leaves grey-green, glaucous; bracts dark brown, hirsute


10: Leaves green, not glaucous; bracts green or dark brown, glabrous to moderately hirsute


11 Spike 2 or more times length of scape; bracts green, glabrous to subglabrous (W.A.)


11: Spike less than 2 times length of scape; bracts dark brown, glabrous to moderately hirsute (eastern mainland Australia)


12 Leaves blue-green or greyish, glaucous


12: Leaves green, not glaucous


13 Cluster-bracts prominent for most or all of mature spike length; packing-bracts dark-brown (eastern Australia)


13: Cluster-bracts prominent only at base of mature spike; packing-bracts light-brown (central Australia & inland W.A.)


14 Scape diam. 20–30 mm; leaves soft and spongy to the touch


14: Scape diam. 20 mm or less; leaves tough, hard to the touch


15 Trunk usually none, sometimes to 30 cm long; crown ±hemispherical (N.S.W., Hunter R. to Sydney region)


15: Trunk usually longer than 30 cm; crown with young leaves in spreading upright tuft and old leaves usually strongly reflexed over trunk (Qld, & N.S.W. north of Hunter R.)


16 Packing-bracts narrowly triangular to subulate


16: Packing-bracts obtuse to triangular


17 Packing-bracts fringed with hairs to moderately hirsute


17: Packing-bracts glabrous or subglabrous


18 Plants without trunk; leaves depressed-obtrullate to depressed-cuneate in T.S. (Tas.)


18: Plants with trunk; leaves quadrate-rhombic in T.S. (W.A.)


19 Packing-bracts densely hirsute on abaxial surface, appearing velvety


19: Packing-bracts glabrous to hirsute or fringed with hairs but not velvety


20 Leaves transverse-rhombic in T.S.; spike dark-brown velvety at flowering


20: Leaves depressed-obtrullate to concave in T.S.; spike cream to ±light brown velvety at flowering


21 Leaves very depressed-cuneate to concave in T.S., 3–6 mm wide, 1.5–2 mm thick (N.S.W., Sydney & southwards)


21: Leaves depressed-obtrullate to depressed-cuneate in T.S., 1.9–3.5 mm wide, 1–1.5 mm thick (Qld, & N.S.W. north of Wyong)


22 Scape and spike together usually less than 90 cm long


22: Scape and spike together usually 90 cm or more long


23 Scape and spike distinctly curved; spike often at ±90° to scape (W.A.)


23: Scape emerging from crown ±vertically; spike and scape ±straight


24 Leaves quadrate-rhombic in T.S. (S.A.)


24: Leaves ranging from transverse-rhombic, depressed-obtrullate to very depressed-cuneate or transverse-linear in T.S.


25 Cluster-bracts prominent on spike


25: Cluster-bracts obscure or restricted to junction of scape and spike


26 Packing-bracts triangular to narrowly triangular (Tas.)


26: Packing-bracts shortly acute to acute


27 Leaves depressed-cuneate in T.S., often concave, green, not glaucous; cluster-bracts shortly acute to triangular (eastern mainland Australia)


27: Leaves transverse-rhombic or depressed-obtrullate in T.S., rarely depressed-cuneate, greyish, glaucous; cluster-bracts narrowly triangular to subulate


28 Crown-leaves broadly spreading or recurved (Qld)


28: Crown an erect tuft of leaves (W.A. & SE Australia)


29 Scape and spike together usually more than 80 cm long (W.A.)


29: Scape and spike together usually less than 75 cm long (eastern mainland Australia)


30 Cluster-bracts usually prominent at least in some part of spike


30: Cluster-bracts obscure or restricted to junction of scape and spike


31 Leaves usually more than 2.5 mm wide, soft and spongy; plant of moist habitats


31: Leaves usually 2.5 mm wide or less, tough and hard; plant of dry sclerophyll forest and heath


32 Leaves usually ±quadrate-rhombic to transverse-rhombic in T.S., less than 3 mm wide


32: Leaves narrowly transverse-rhombic, depressed-obtrullate, depressed-cuneate to transverse-linear or concave in T.S., 1.7–10 mm wide


33 Trunk none or to 30 cm long; crown ±hemispherical (N.S.W., Sydney region and adjacent areas south of the Hunter R.)


33: Trunk 10 cm to 5 m long; crown with young leaves in spreading upright tuft, old leaves usually strongly reflexed over trunk (Qld & N.S.W. north of the Hunter R.)


34 Leaves blue-green


34: Leaves green


35 Spike usually greater than 1/2 or as long as scape in length


35: Spike usually less than 1/2 as long as scape


36 Leaves usually more than 4 mm wide; spike 30–150 cm long


36: Leaves usually less than 4 mm wide; spike usually 5–40 cm long


37 Spike 20–40 mm diam.; petals without proboscis (W.A.)


37: Spike 14–23 mm diam.; petals with proboscis (Qld)



Data derived from Flora of Australia Volume 46 (1986), a product of ABRS, ©Commonwealth of Australia