Araceae

Araceae Temporal range: 70–0 Ma PreЄ Є O S D C P T J K Pg N Late Cretaceous - Recent
Flower of Xanthosoma sagittifolium
Scientific classification
Kingdom:	Plantae
Clade:	Angiosperms
Clade:	Monocots
Order:	Alismatales
Family:	Araceae Juss.
Genera
Main article: List of Araceae genera

Snake lily (Dracunculus vulgaris) in Crete, Greece.

Peace lily (Spathiphyllum cochlearispathum) clearly showing the characteristic spadix and spathe.

The Araceae are 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 aroids. 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 northern temperate regions. A comprehensive genomic study of Spirodela polyrhiza was published in February 2014.

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, due to the efforts of researcher and aroid authority Josef Bogner.

Description

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. Some species are dioecious.

Many plants in this family are thermogenic (heat-producing). Their flowers can reach up to 45°C 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, to attract flies to pollinate the plant. The heat produced by the plant helps to convey the scent further.

Taxonomy

Classification

One of the earliest observations of species in Araceae was conducted by Theophrastus in his work Enquiry into Plants. The Araceae were not recognized as a distinct group of plants until the 16th century. In 1789, Antoine Laurent de Jussieu classified all climbing aroids as Pothos and all terrestrial aroids as either Arum or Dracontium in his book Familles des Plantes.

The first major system of classification for the family was produced by Heinrich Wilhelm Schott, who published Genera Aroidearum in 1858 and Prodromus Systematis Aroidearum in 1860. Schott's system was based on floral characteristics, and used a narrow conception of a genus. Adolf Engler produced a classification in 1876, which was steadily refined up to 1920. His system is significantly different from Schott's, being based more on vegetative characters and anatomy. The two systems were to some extent rivals, with Engler's having more adherents before the advent of molecular phylogenetics brought new approaches.

Modern studies based on gene sequences show the Araceae (including the Lemnoideae, duckweeds) to be monophyletic, and the first diverging group within the Alismatales. The APG III system of 2009 recognizes the family, including the genera formerly segregated in the Lemnaceae. The sinking of Lemnaceae into Araceae is not universally accepted. For example, the 2010 New Flora of the British Isles uses a paraphyletic Araceae and a separate Lemnaceae.

Genera

Main article: List of Araceae genera

The cuckoo-pint or lords and ladies (Arum maculatum) is a common arum in British woodlands

Arisaema triphyllum

Anthurium and Zantedeschia are two well-known members of this family, as are Colocasia esculenta (taro) and Xanthosoma roseum (elephant ear or ‘ape). The largest unbranched 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 Colocasia esculenta (taro) and Monstera deliciosa provide food value; the fruit of M. deliciosa is 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 eastern 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.

Toxicity

Within the Aracae, genera such as Alocasia, Arisaema, Caladium, Colocasia, Dieffenbachia, and 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, with the symptoms occurring for up to two weeks.

See also

List of foliage plant diseases (Araceae)

Further reading

• Bown, Deni (2000). Aroids: Plants of the Arum Family [ILLUSTRATED]. Timber Press. ISBN 0-88192-485-7
• online

External links

• International Aroid Society
• Araceum - Plants of the Araceae Family - The Illustrated Database
• The Uberlist of Araceae (pdf)
• list of publications (March 2008) for Dr. h.c. Josef Bogner