Monocots

Only a few genera in four monocot families in three orders produce resin (Figure 2-5). Two families, Convallariaceae and Xanthorrhoeaceae, are in the order Asparagales. The Arecaceae (or Palmae) are the sole family in the commelinoid order Arecales with a resin producer. Araceae (order Alisma-tales) produce a chemical substance that has not been substantiated as a resin. The resin of all producing monocot species, except in the Araceae, is phenolic based.

Species of the large tropical genus Dracaena are put by APG in the Convallariaceae (Liliaceae s.l.). However, they are often placed in Dracaenaceae (Agavaceae in the sense of Cronquist 1981). Evergreen shrubby Dracaena species are familiar to many as indoor and greenhouse ornamentals and are grown outdoors in the tropics and subtropics. Most species are native to warm arid areas and may occur as trees. The name, from the Greek drakoina, female dragon, alludes to the massive trunks and branches of the dragon tree (D. draco); the red phenolic resin produced is known as dragon's blood. Dracaena draco is the most massive species of the genus, often growing 12-19 m high. A notable specimen (Figure 2-6) growing in Tenerife, Canary Islands, was 22 m high, had a trunk girth of nearly 14 m, and was thought to be the oldest tree in the world by ancient peoples (Everett 1981). It was alleged to be 6000 years old in 1868, but in 1991 no plant more than 365 years was found alive (Mabberley 1997). The resin, collected from incisions of the stems of several other Dracaena species from Somalia and the island of Socotra, was used pharmaceutically and for coloring varnishes (Chapter 10).

In the family Xanthorrhoeaceae (Rudall and Chase 1996), the single Australian endemic genus Xanthorrhoea produces a yellow or red phenolic acaroid resin. In fact, the name Xanthorrhoea was derived from the Greek xanthas (yellow) and rhoea (flowing), referring to the yellow resin noted in the type species, X. resinífera. Xanthorrhoea trees are a characteristic feature of the vegetation in many parts of Australia. They grow slowly and usually attain a height of 2-3 m before branching into a tuft of grass-like leaves about a meter long. As the plants grow, the basal leaf bases remain attached to the fibrous trunk, making the plant look like a small palm at a distance. The tuft of grass-like leaves and the tree-like appearance led to the plant's common name, grass tree (Plate 12); it is sometimes called black boy because of a fire-blackened trunk. It is very resistant to fire, especially when young, because the bud is 12 cm below the ground; later buds are protected by old leaves. Some species such as X. preissii live at least 350 years, and flowering may be delayed until 200 years. Flowering is stimulated by fire, however, and some species growing near human habitations flower more frequently because more fires occur there. The resin, which accumulates in the old leaf bases of several species, has been used commercially for various purposes (Chapter 10).

The Arecales is the sole order of commelinoids in which resin is produced, and its occurrence is restricted to only one genus of the palm family (Are-

Figure 2-6. The very large, legendary dragon tree, Dracaena draco, in Tenerife, Canary Islands, drawn from a photograph of a mural painted by Charles Corwin in the Field Museum of Natural History, Chicago.

caceae). Although palm fruits are better known for their true oils, a distinct group of climbing species of the large Indomalesian rattan genus Daemo-norops (Figure 2-7) produces a red resin on the surface of unripe fruits (Plate 47) that has been used medicinally and for colored varnish (Chapter 10). Like the red resin from Dracaena, it has been called dragon's blood and has been the most important commercial source of this kind of red resin.

The aroids (Araceae) Philodendron and Monstera produce a sticky mate rial in the flowers that has been called resin, but the chemical components

Figure 2-7. The Indomalesian scandent spiny rattan palm Daemonorops has a red resin called dragon's blood that covers the unripe fruit (Plate 47).

Figure 2-7. The Indomalesian scandent spiny rattan palm Daemonorops has a red resin called dragon's blood that covers the unripe fruit (Plate 47).

have not been analyzed. Grayum (1996) stated that this "resinous secretion" in the spathes of most species of Philodendron subgenus Pteromischum probably functions primarily in the adhesion of pollen to the exoskeleton of pollinating dynastine scarab beetles. Resin-gathering trigonid bees also collect "resin" from Monstera flowers for nest construction (Ramírez and Gómez 1978). However, Grayum (1996) was unaware of resin-gathering bees involved in pollination of Philodendron whereas such bees are involved in the pollination of Clusia (Clusiaceae) and Dalechampia (Euphorbiaceae) (Chapter 5). Better understanding of the chemical nature and role of this secretion awaits further study.

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