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, 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. 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 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, Amorphophallus titanum, Amorphophallus paeoniifolius,
Helicodiceros muscivorus and Sauromatum venosum. 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 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=
Anthurium and Zantedeschia are two well-known members of this family, as
are Colocasia esculenta and Xanthosoma roseum. The largest unbranched
inflorescence in the world is that of the arum Amorphophallus titanum. 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 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 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 References
Further reading Bown, Deni. Aroids: Plants of the Arum
Family [ILLUSTRATED]. Timber Press. ISBN 0-88192-485-7
Croat, Thomas B. "History and Current Status of Systematic Research with
Araceae". Aroideana 21. online Grayum, Michael H. "Evolution and
Phylogeny of the Araceae". Annals of the Missouri Botanical Garden 77.
doi:10.2307/2399668. Keating R C. "Vegetative anatomical data
and its relationship to a revised classification of the genera of
Araceae". Annals of the Missouri Botanical Garden 91: 485–494. JSTOR
3298625. External links
International Aroid Society Araceum - Plants of the Araceae Family -
The Illustrated Database The Uberlist of Araceae
list of publications for Dr. h.c. Josef Bogner