Spotlight on: Trithrinax

Germany's Tobias Spanner takes a look at this much under-used palm genus, containing some of the world's most beautiful hardy palms.
Tobias Spanner, Tizianstrasse 44, 8000 München 19, Germany
Chamaerops No. 8, published online 23-10-2002

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Heavily armed: Thritrinax campestris

The genus Trithrinax comprises five species of small to moderate, solitary or clustering fan-palms from northern Argentina, southern Brazil, Bolivia, Paraguay and Uruguay, where they occur mostly in savannah-like dry forest vegetation (Chaco).

Trithrinax is considered one of the most primitive palm genera which could well be looked at as a palm prototype especially in its reproductive parts (info re sc en c e, flowers and fruit). Its closest relatives are two even less known rare palms from tropical South America, Itaya and Cryosophila, the Root Spine Palms.

All species are easily recognised by their characteristic heavy armament with very spiny fibrous leaf sheaths, which persist on the stem, and gives them formidable protection. Eventually, on older specimens, the sheaths are shed to reveal a slender, roughly ringed trunk.

The stem carries a small to medium crown of stiff, circular, regularly palmate leaves, which are rather flat, not costopalmate and in most species beautifully glaucous on one or both sides. Inflorescences appear in late winter or early spring and produce clusters of showy, mostly white or yellow fruits in autumn, which hang down in bunches like grapes. Being hermaphroditic, even a single plant can produce seeds.

The species you are most likely to come across is Trithrinax acanthocoma, the 'Spiny Fibre Palm', the largest one in the genus, from southern Brazil and Paraguay.

This very ornamental and unusual plant develops a robust trunk about 20 cm in diameter and 4 metres or more tall, densely covered with spines from persistent leaf sheaths, topped by a crown of large, mid-green to slightly glaucous fan-leaves divided into broad, pointed, sometimes drooping segments. The fleshy, yellow white fruits are 22.5cm in diameter, and grow in large bunches.

Trithrinax acanthocoma occurs in an area with warm summers and mild winters and experiences daily occasional light to medium frosts. The climate is rather dry with rainfall, which is more or less evenly distributed throughout the year.

A similar but smaller species is Trithrinax brasiliensis. It is said to be nearly extinct in its native habitat in southeast Brazil, northeast Argentina and possibly Uruguay. It has deeply divided leaf blades of medium size, similar to Trachycarpus fortunei, green above and glaucous below, and the leaflets are bifid at the apex.

The solitary or sometimes caespitose stems are slender, 7-15cm in diameter and up to 4 metres tall. The black fruits are round, small, 0.8cm in diameter. Climatic conditions are warm temperate, similar to T. acanthocoma.

My personal favourite in the genus is the extremely desirable Trithrinax campestris from north-eastern Argentina, a very hardy species which grows as a clump of several short prostrate or erect trunks to about 2 metres tall, with small, very stiff, silvery-grey leaves. It is viciously armed not only with its fibrous stem but also with long spikes on the tips of the leaflets. Fruits are the size of T. acanthocoma.

The climate is warm temperate with only occasional light to medium frosts.

Further inland in northern Argentina and western Paraguay grows another beautiful, small, caespitose species, the very rare Trithrinax biflabellata. Found in wetter, semi-dry situations in sandy marshes or along riverbanks, often on saline soils and in a warmer climate with hot summers and warm winters and only occasional medium frosts. It is probably the best species for cultivation indoors.

It develops very slender, curving trunks, sometimes to 5 metres high. The rather small, narrow leaf-blade has a deep central division almost to the base. Fruits are globose, about 1 cm in diameter.

Finally, there is Trithrinax schizophylla, a rather tall, robust, caespitose species, which reaches the foothills of the Andes in its distribution area from northwestern Argentina, southern Bolivia to southeastern Brazil. It grows in an arid climate with hot summers and mild winters with occasional medium frosts.

The plant grows several tall trunks up to 5 metres high and I 5-20cms in diameter, densely covered in spiny leaf sheaths as all Trithrinax. Leaves are rigid and of medium size. The fruits are small, 0.8 cms in diameter and a yellow-green colour.

Trithrinax are very adaptable and rewarding subjects for cultivation, and particularly attractive ornamentals for their rigid, often glaucous leaves and the finely netted leaf sheaths, but, unfortunately, besides T. acanthocoma, which is occasionally seen, all species are rare in cultivation.

All Trithrinax are exceedingly cold tolerant and can be grown outside all around the Mediterranean with little protection, and even in milder parts of northern Europe. They will grow well even in areas with cooler summers with the possible exception of T. biflabellata, and will withstand even heavier frosts. T. acanthocoma will be unharmed down to -9°C and T. campestris has been reported to withstand temperatures from 50 down to - I 20C. The other species should be just as hardy as indicated by the occurrence of frost in their native habitats.

Although they are very resistant to drought, for best results, all species should be kept well watered in the summer and not too heavily fertilized. In winter, plants especially those in containers, should be kept rather dry. Trithrinax needs fresh air and resents damp conditions in winter. When planted in areas with cold, moist winters, plants might require some protection against heavy rain, or snowfall.

The biggest problem with Trithrinax is still getting hold of plants or seeds. Even small plants are rarely available as are seeds, and germination unfortunately is not too easy. If you are lucky enough to get seeds, soak them for a few days and then sow at 25-30 C. With fresh seeds, the first seedlings should appear after 2-3 months but may also take much longer, more than a year is not unusual, so patience is required.

The small rigid leaved species will grow on very slowly but at least T. acanthocoma and T. brasiliensis will do a quite bearable rate. They can flower when still quite young. Deep pots are advisable for maximum growth.

Trithrinax are spectacular, very ornamental and unusual, tough, robust house-tub or outdoor palms which can be grown in most conditions without major difficulties. Highly recommended!

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