Araceae: The Arum Family Flowers
Araceae is a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe or leaf-like bract. Also known as the Arum family, members are often colloquially known as aroid. This family of 107 genera and over 3700 species is most diverse in the New World tropics, although also distributed in the Old World tropics and north temperate regions.
One of the earliest observations of species in Araceae was conducted by Theophrastus in his work Enquiry into Plants. It wasn't until the 16th century that Araceae was recognized as a distinct group of plants. In 1789 Antoine Laurent de Jussieu classified all climbing aroids as Pothos and all terrestrial aroids as either Arum or Dracontium in his book Families des Plantes. It wasn't until Heinrich Wilhelm Schott published Genera Aroidearum in 1858 and Prodromus Systematis Aroidearum in 1860 that major classification progress was made in the family. At the time of writing these books Schott was only aware of approximately 900 species that he subsequently classified into 12 tribes. These 12 tribes grew to become the primary framework from which all subsequent classification was based.
The largest collection of living Araceae is maintained at Missouri Botanical Gardens. Another large collection of living Araceae can be found at Munich Botanical Garden, thanks to the efforts of the researcher and aroid authority Josef Bogner.
Anthurium and Zantedeschia are two well-known members of this family, as are Colocasia esculenta (taro) and Xanthosoma roseum (Elephant ear or ‘ape). Among the largest inflorescence in the world is that of the arum Amorphophallus titanum (Titan arum). The family includes many ornamental plants: Dieffenbachia, Aglaonema, Caladium, Nephthytis, and Epipremnum, to name a few. In the genus Cryptocoryne are many popular aquarium plants. Both Taro and Monstera deliciosa provide food value (the fruit of Monstera deliciosa called "Mexican breadfruit"). Philodendron is an important plant in the ecosystems of the rainforests and is often used in home and interior decorating. Symplocarpus foetidus (skunk cabbage) is a common North American species. An interesting peculiarity is that this family includes the largest unbranched inflorescence, that of the titan arum, often erroneously called the "largest flower" and the smallest flowering plant and smallest fruit, found in the duckweed, Wolffia. Recent genetic research by the Angiosperm Phylogeny Group has shown that the duckweeds, previously treated in a separate family Lemnaceae, also belong in the Araceae family.
Species in Araceae are often rhizomatous or tuberous and are often found to contain calcium oxalate crystals or raphides. The leaves can vary considerably from species to species. The inflorescence is composed of a spadix, which is almost always surrounded by a modified leaf called a spathe. In monoecious aroids (possessing separate male and female flowers, but with both flowers present on one plant), the spadix is usually organized with female flowers towards the bottom and male flowers towards the top. In aroids with perfect flowers the stigma is no longer receptive when the pollen is released, thus preventing self-fertilization. There are also some dioecious species.
Many plants in this family are thermogenic (heat-producing). Their flowers can reach up to 45 degrees Celsius even when the surrounding air temperature is much lower. One reason for this unusually high temperature is to attract insects (usually beetles) to pollinate the plant, rewarding the beetles with heat energy. Another reason is to prevent tissue damage in cold regions. Some examples of thermogenic Araceae are: Symplocarpus foetidus (eastern skunk cabbage), Amorphophallus titanum (Titan Arum), Amorphophallus paeoniifolius (elephant foot yam), Helicodiceros muscivorus (dead horse arum lily) and Sauromatum venosum (voodoo lily). Species such as Titan Arum and the dead horse arum give off a very pungent smell, often resembling a rotten animal. This is to attract flies to pollinate the plant. The heat produced by the plant helps to convey the scent further.
Within the Araceae, genera such as Alocasia, Arisaema, Caladium, Colocasia, Dieffenbachia, Philodendron contain calcium oxalate crystals in the form of raphides. When consumed, these may cause edema, vesicle formation and dysphagia accompanied by painful stinging and burning to the mouth and throat, the symptoms occurring for up to two weeks. [source : Araceae]