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Genus Xanthorrhoea Family Xanthorrhoeaceae
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).


Habitat
Photo D. Hardin

Flower
Photo D. Hardin

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 
1Scape 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 chambersXanthorrhoea 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 pits2
2Spike longer than scape3
Spike shorter than or as long scape
                       Back to 1
8
3Packing bracts subulate, glabrousXanthorrhoea australis
Packing bracts shortly acute to triangular, glabrous to hirsute or fringed with hairs
                       Back to 2
4
4Cluster bracts obscure or almost soXanthorrhoea media
Cluster bracts prominent for at least part of spike
                       Back to 3
5
5Leaves blue-green or greyish, glaucousXanthorrhoea glauca
Leaves green, not glaucous
                       Back to 4
6
6Scape usually 20–30 mm diam.; leaves soft and spongy to the touchXanthorrhoea malacophylla
Scape usually less than 20 mm diam.; leaves tough, hard to the touch
                       Back to 5
7
7Trunk usually absent, sometimes to 30 cm long; crown more or less hemispherical; Hunter R. to Sydney regionXanthorrhoea 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
8Packing bracts densely hirsute on outer surface, appearing velvety9
Packing bracts glabrous to hirsute or fringed with hairs but not velvety
                       Back to 2
11
9Leaves transverse-rhombic in T.S.; spike dark brown velvety at floweringXanthorrhoea resinosa
Leaves depressed-obtrullate to concave in T.S.; spike cream to more or less light brown velvety at flowering
                       Back to 8
10
10Leaves very depressed-cuneate to concave in T.S., 3–6 mm wide, 1.5–2 mm thick; south from Sydney districtXanthorrhoea 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
11Scape and spike together usually less than 90 cm long12
Scape and spike together usually 90 cm or more long
                       Back to 8
14
12Cluster bracts prominent on spike13
Cluster bracts obscure or restricted to junction of scape and spike
                       Back to 11
Xanthorrhoea minor
13Leaves depressed-cuneate in T.S., often concave, green, not glaucous; cluster bracts shortly acute to triangularXanthorrhoea 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
14Cluster bracts usually prominent at least in some part of spike15
Cluster bracts obscure or restricted to junction of scape and spike
                       Back to 11
16
15Leaves usually more than 2.5 mm wide, soft and spongy; grows in moist habitatsXanthorrhoea malacophylla
Leaves usually 2.5 mm wide or less, tough and hard; grows in dry sclerophyll forest and heath
                       Back to 14
Xanthorrhoea johnsonii
16Leaves usually more or less quadrate-rhombic to transverse-rhombic in T.S., less than 3 mm wide17
Leaves narrowly transverse-rhombic, depressed obtrullate, depressed-cuneate to transverse-linear or concave in T.S
                       Back to 14
18
17Trunk absent or to 30 cm long; crown more or less hemispherical; south of the Hunter RXanthorrhoea 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
18Spike usually more than half or as long as scapeXanthorrhoea arborea
Spike usually less than half as long as scape
                       Back to 16
Xanthorrhoea latifolia

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