|Chamaerops humilis var. humilis, Zingaro, Sicily|
|Large monospecific patch of C. humilis in SW Spain.|
It is one of only two palm species, along with Phoenix theophrasti, native to southern Europe. It is mainly found in southwestern Europe (Malta, Sicily, over all the Mediterranean coast of Spain and Portugal, central and southern Italy, some parts of the southern Mediterranean coast of France, as well as northwest Africa (Morocco, Algeria, Tunisia). It is the northernmost naturally occurring palm in the world, with the northernmost localities at Hyères-les-Palmiers, at 43° 07' N, and on the island of Capraia off the Italian coast, at 43° 04' N.
It is a shrub-like clumping palm, with several stems growing from a single base. The stems grow slowly and often tightly together, eventually reaching 2–5 m tall with a trunk diameter of 20–25 cm. It is a fan palm (Arecaceae tribe Corypheae), with the leaves with a long petiole terminating in a rounded fan of 10–20 leaflets; each leaf is up to 1–1.5 m long, with the leaflets 50–80 cm long. It also has numerous sharp needle-like spines produced on the leaf stems; these may protect the stem growing point from browsing animals. The flowers are borne in dense, short inflorescences at the top of the stems; it is usually (but not invariably) dioecious with male and female flowers on separate plants. The prophyll covers the flowers until the sexual phase (anthesis) and then splits open apically into two triangular lobes. The number of flowers per inflorescence is highly variable for both male and female plants, depending on the size of the inflorescence. Female flowers are tri-ovulate. Unripe fruits are bright green, turning to dull yellow to brown when ripe during the fall (September–November). The seed (usually 0.6–0.8 g) comprises a small cylindrical embryo, which is surrounded by several layers, from inner to outer: (1) a nutritious endosperm, (2) a wide woody layer or endocarp, (3) a fleshy and fibrous mesocarp (the pulp), and (4) the thin outer layer or exocarp. It has an underground rhizome which produces shoots with palmate, sclerophyllous leaves.
- Chamaerops humilis var. argentea André (syn. C. h. var. cerifera) – "Atlas mountain palm" of Northwest Africa. Leaves glaucous.
- Chamaerops humilis var. epondraes – Northwest Africa. Leaves glaucous.
- Chamaerops humilis var. humilis – Southwest Europe. Leaves green.
- Chamaerops humilis 'Vulcano' – Compact, thornless cultivar. May be silvery, but less so than argentea. The leaves tend to be thicker, and the appearance of the plant is bushier than var. humilis or var. argentea.
It is closely related to the genus Trachycarpus from Asia, differing in clumping habit (Trachycarpus only forms single stems without basal suckers), the spiny leaf stems (spineless in Trachycarpus), and in small details of the flower anatomy.
C. humilis is used in gardening and landscaping in many parts of the world. In temperate regions it is usually cultivated as a houseplant, though in sheltered areas it will survive short periods below freezing point.
Ecology and interactions with animals
It is adapted to a Mediterranean climate with cool, moist winters and hot and sunny summer conditions with periodic drought. It can grow on poor and rocky soils. It is one of the hardier palms, tolerating winter frosts down to about −12°C.
It flowers in April–May and is pollinated by a specific weevil, Derelomus chamaeropsis F. (Curculionidae), and perhaps also by wind. C. humilis is engaged in a nursery pollination mutualism with D. chamaeropsis. At anthesis, both male and female plants attract pollinators with floral-like chemical compounds that curiously are released by leaves, and not by flowers. Once pollinating weevils have found a plant (either male or female), they typically stay on the same plant until the end of its anthesis, finding shelter, egg-laying sites and food within inflorescences. When the host plant reaches the end of anthesis, weevils leave the plant and forage to find a new host plant, either male or female. Larval development occurs within rachises of inflorescences of male plants during autumn and winter. At the beginning of the next flowering period, adult weevils emerge from the dry and brittle stems of old inflorescences of the previous year of male plants. Weevils have been shown to lay eggs within female inflorescences, but as soon as seeds start to develop, eggs or larvae are destroyed.
The ripe pulp of C. humilis has several intriguing ecological functions. First, when ripened, the pulp smells strongly of rancid butter and thus acts as a foraging cue for nocturnal frugivores (e.g., mammalian carnivores such as badgers and foxes). Second, it has a germination inhibitory function, ensuring that the seed does not germinate until has been dispersed. And third, the pulp also acts as a chemical and/or physical barrier against invertebrate seed predators (curculionoid beetles). Because of such pulp multifunctionality, fruit ingestion (and thus pulp removal) by carnivores can have both positive and negative consequences for the palm. On the one hand, seeds ingested by carnivores germinate more frequently than non-ingested seeds. On the other hand, ingested seeds experience higher predation by invertebrates than non-ingested seeds. However, because of the high mobility of carnivores, their dispersal service appears paramount given the severe fragmentation and isolation of most C. humilis populations across the highly humanized Mediterranean basin.
Uses and threats
Due to its rusticity and resprouting ability after fire, it has a high ecological value for preventing erosion and desertization. This charismatic palm is thus considered one of the most important species in the natural conformation of the "garrigues" and "macchias" of the Mediterranean coastline.
The leaves of the adult plants have been used in basketweaving to make mats, carrier baskets, and brooms. The young unopened leaves are treated with sulphur to make them softer and supple and are then used for finer work. The husk, known in southern Spain as "higa", is edible before its full development. The fruits are not edible but have been traditionally used in medicine as an astringent because of their bitterness and high tannin content.
Because its natural habitat is rapidly declining due to urbanization and other human activities, conservation concerns and protection regulations of this Mediterranean endemism are rising. In some areas, including its northernmost native location, it is seriously threatened by an introduced South American moth Paysandisia archon.
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- WCSP, World Checklist of Palms: Chamaerops
- Euro+Med Plantbase Project: Chamaerops humilis
- Parcs Nationaux de France: Hyères-les-(ex)-Palmiers
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- Fedriani, J.M., and M. Delibes. 2011
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- Merlo M.E., M.M. Aleman, J. Cabello, and J. Penas. 1993. On the Mediterranean Fan Palm (Chamaerops humilis). Principes 37: 151-8.
- International Palm Society: Importation of Mature Palms: A Threat to Native and Exotic Palms in Mediterranean Countries?
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