Common Name: Grass trees
Description: Perennials with stems arborescent or subterranean, woody, covered with packed leaf bases.
Leaves crowded in a terminal crown, narrow-linear, tapered, rhombic to cuneate in T.S.; margins with microscopic trichomes, rarely hairy; leaf base broad, sometimes thickened.
Inflorescence cylindrical, spike-like, on a woody scape; flowers in spirally arranged clusters subtended by cluster bracts and surrounded by packing bracts that fill out the spaces between the flowers and form the surface of the spike. Flowers actinomorphic, 3-merous, bisexual and either fertile or aborted. Tepals 6, free, in 2 whorls; outer tepals papery or scarious; inner tepals membranous, apices exserted. Stamens 6, longer than tepals; filaments flattened; anthers dorsifixed, 2-locular, introrse, dehiscing by longitudinal slits. Septal nectaries exude copious nectar. Ovary superior, 3-locular; ovules several per loculus; style simple; stigma entire, sometimes grooved.
Fruit a capsule, obtuse or pointed, the hardened style base ± exserted; seeds 1 or 2 per loculus, ovate, usually semi-matt black, rarely ovoid and shining (in 1 species).
Distribution and occurrence: World: 28 species, endemic Australia. Australia: all States.
Hybrids occasionally occur on coastal sand dunes, north from Newcastle between several species. Other plants that have been reported as hybrids in the past may be unrecognised new species or may be just part of the variation of existing species. Plants of Xanthorrhoea are often very long-lived; some are estimated to be 350-450 years old. Studies of species that develop tall trunks indicate that increase in trunk height is mostly slow, about 0.8-6 cm per year , but this varies depending on the species and on local growth conditions. A useful report 'Xanthorrhoea: A review of current knowledge with a focus on X. johnsonii and X. latifolia, two Queensland protected plants-in-trade' by A.C. Borsboom (2005) summarises what is known for all species to that date. (An online version of the report can be viewed here.)
Text by D. J. Bedford (1993); edited KL Wilson (July 2009)
Taxon concept:
| | Key to the species | |
| 1 | Scape more than 7 times as long as spike; flowering spike broad and brush-like from the very long erect filaments; stomates in linear, subsurface, hair-lined chambers | Xanthorrhoea macronema |
| Scape less than 6 times as long as spike; flowering spike more or less cylindrical, the filaments short and erect or, if longer, recurved; stomates at leaf surface or if sunken, then in pits | 2 |
| 2 | Spike longer than scape | 3 |
| Spike shorter than or as long scape
Back to 1 | 8 |
| 3 | Packing bracts subulate, glabrous | Xanthorrhoea australis |
| Packing bracts shortly acute to triangular, glabrous to hirsute or fringed with hairs
Back to 2 | 4 |
| 4 | Cluster bracts obscure or almost so | Xanthorrhoea media |
| Cluster bracts prominent for at least part of spike
Back to 3 | 5 |
| 5 | Leaves blue-green or greyish, glaucous | Xanthorrhoea glauca |
| Leaves green, not glaucous
Back to 4 | 6 |
| 6 | Scape usually 20–30 mm diam.; leaves soft and spongy to the touch | Xanthorrhoea malacophylla |
| Scape usually less than 20 mm diam.; leaves tough, hard to the touch
Back to 5 | 7 |
| 7 | Trunk usually absent, sometimes to 30 cm long; crown more or less hemispherical; Hunter R. to Sydney region | Xanthorrhoea media |
| Trunk usually more than 30 cm long; crown with young leaves in spreading upright tuft and old leaves usually strongly reflexed over trunk; north of Hunter R
Back to 6 | Xanthorrhoea johnsonii |
| 8 | Packing bracts densely hirsute on outer surface, appearing velvety | 9 |
| Packing bracts glabrous to hirsute or fringed with hairs but not velvety
Back to 2 | 11 |
| 9 | Leaves transverse-rhombic in T.S.; spike dark brown velvety at flowering | Xanthorrhoea resinosa |
| Leaves depressed-obtrullate to concave in T.S.; spike cream to more or less light brown velvety at flowering
Back to 8 | 10 |
| 10 | Leaves very depressed-cuneate to concave in T.S., 3–6 mm wide, 1.5–2 mm thick; south from Sydney district | Xanthorrhoea concava |
| Leaves depressed-obtrullate to depressed-cuneate in T.S., 1.9–3.5 mm wide, 1–1.5 mm thick; north of Wyong
Back to 9 | Xanthorrhoea fulva |
| 11 | Scape and spike together usually less than 90 cm long | 12 |
| Scape and spike together usually 90 cm or more long
Back to 8 | 14 |
| 12 | Cluster bracts prominent on spike | 13 |
| Cluster bracts obscure or restricted to junction of scape and spike
Back to 11 | Xanthorrhoea minor |
| 13 | Leaves depressed-cuneate in T.S., often concave, green, not glaucous; cluster bracts shortly acute to triangular | Xanthorrhoea minor |
| Leaves transverse-rhombic or depressed-obtrullate in T.S., rarely depressed-cuneate, greyish, glaucous; cluster bracts narrow-triangular to subulate
Back to 12 | Xanthorrhoea acaulis |
| 14 | Cluster bracts usually prominent at least in some part of spike | 15 |
| Cluster bracts obscure or restricted to junction of scape and spike
Back to 11 | 16 |
| 15 | Leaves usually more than 2.5 mm wide, soft and spongy; grows in moist habitats | Xanthorrhoea malacophylla |
| Leaves usually 2.5 mm wide or less, tough and hard; grows in dry sclerophyll forest and heath
Back to 14 | Xanthorrhoea johnsonii |
| 16 | Leaves usually more or less quadrate-rhombic to transverse-rhombic in T.S., less than 3 mm wide | 17 |
| Leaves narrowly transverse-rhombic, depressed obtrullate, depressed-cuneate to transverse-linear or concave in T.S
Back to 14 | 18 |
| 17 | Trunk absent or to 30 cm long; crown more or less hemispherical; south of the Hunter R | Xanthorrhoea media |
| Trunk 10 cm to 5 m long; crown with young leaves in spreading upright tuft, old leaves usually strongly reflexed over trunk; north of the Hunter R
Back to 16 | Xanthorrhoea johnsonii |
| 18 | Spike usually more than half or as long as scape | Xanthorrhoea arborea |
| Spike usually less than half as long as scape
Back to 16 | Xanthorrhoea latifolia |
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