Plants of the World Online (Kew) has them in family Asparagaceae but they are still seen in other families.
L. longifolia var. longifolia is a synonym for the Spiny-head Mat-rush.
The Australian natives are perennial herbs growing from underground stems or rhizomes.
New plants growing along the rhizomes form large dense clumps or tussocks.
The shiny green basal leaves are in 2 ranks (distichous).
The strap-like leaves are mostly 50 to 100 cm long and 7 to 8 (2 to 12) mm wide.
The blade can be flat or slightly rolled under, the edges are smooth and the veins prominent.
The leaf tips typically have 2 or 3 prominent teeth which are important in identification.
The lateral teeth, close the the tip are usually shorter than tip but may be longer.
There are always deep notches or sinuses between them all.
The edge of the wide basal leaf sheath is smooth or frayed into thick strands.
It can be brown, reddish-brown or rarely white.
The flowers are unisexual with males and females on different plants.
Their 30 to 50 cm long inflorescences are similar being a stiff branched spike or panicle.
In panicles the flowers at the base of each branch open first.
The flattened leafless stem or scape is shorter than the branched midrib or rachis.
Along the rachis are whorls of 2 (3 or 4) primary side branches that do not branch again.
There are clusters of stemless flowers at the nodes on the midrib and side branches.
There is a very stiff sharp cluster bract up to 2 cm long at the base of each cluster of flowers.
There are small pale outer and inner bracts under each flower.
Male inflorescence side branches, up to 15 cm long are longer than the female branches.
Male flowers, 3 to 4 mm long are a little shorter than the females that are 4 to 4.5 mm.
Both have flowers with 6 tepals in 2 whorls of three with the inner ones slightly longer.
The outer three (sepals) are brown or purplish and papery in texture.
The inner tepals (petals) are thicker and fleshy and cream or yellow.
Male flowers have 6 stamens with wide filaments.
Female have a 3-loculed ovary and a style with 3 stigma lobes.
The fruit are smooth pale brown loculicidal capsules with 1 to 3 seeds.
Lomandra longifolia subsp. hystrix is a synonym of Lomandra hystrix.
L. hystrix, the Creek Mat-Rush is very similar to L. longifolia but this has secondary branching
in the inflorescences and leaf tips with small side teeth well below the tip without deep sinus between them.