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calamus has been dispersed by this means. The seeds arealso
dispersed by water along stream margins.
Acorus is found mainlyin the northern hemisphere, fromthe
temperate zone to the subtropics and higher altitudes inthe tropics
in Asia, in Europe and North America. A.calamus was widely
dispersed in Europe and parts ofeastern North America by human
agency due to its
medicinal importance and later became naturalized inmany
regions. Records from Celebes (Sulawesi), Philip-pines and New
Guinea (including the Bismarck Archipe-lago) are not able to
confirm if these are natural orintroduced and later naturalized;
but A. calamus iscommon and widespread in the New Guinea
highlands.
Acorus is a herbaceous helophyte which forms densepopulations by
strongly branching rhizomatous stems. Itgrows along margins of
rivers, streams, ponds, lakes,ditches, standing or slow running
water or swampy areas.Acorus is found from sea level to 1100 m in
central Europe(nearly the same altitude in Turkey) and up to 2600 m
inChina. The two species of Acorus are apparently not
threatened and both are easy to grow; A. calamus especiallyis
prone to naturalize easily and become quite weedy underfavourable
conditions.
Fossil History
The family Acoraceae is documented by fossils from theEocene of
North America; it was first described as Acorusheeri by Berry and
later closely studied by Crepet (1977)and transferred to its own
genus as Acorites heeri(Berry)Crepet. The fossil Acorus
brachystachys Heer wasdescribed from the Eocene (not Miocene as
originallyreported) of Spitzbergen and for over a century
wasthought to belong to Acorus, but new material and further
studies showed that this fossil is identical with short shooof
Nordienskioeldia borealis Heer (TrochodendralceaeAcoropsis eximia
(Go pp.&Menge) Bogner (syn. Acoropsminor Conw.) is an
infructescence from the Baltic amber oEocene age, but does not
belong to the Acoraceae; it is member of the AraceaeMonsteroideae,
tribe Monsterea
Phylogeny
Acorus was for a long time considered to be a member othe
Araceae and it has only recently been removed fromthis family,
although the family Acoraceae was describeas early as 1820. There
are significant characters thadistinguish Acorus from the Araceae:
presence of speciaethereal oil cells, absence of raphides, presence
operisperm, cellular endosperm development, trichomeon the
micropyle of the ovules, unifacial leaves, twseparate vascular
systems in the peduncle and a few othe
anatomical characters. DNA studies have shown thaAcorus is a
sister taxon to all other monocots and somauthors believe that it
is the most primitive living monocotoday.
Further Reading
Bogner J and Mayo SJ (1998) Acoraceae. In: Kabitzki K (ed.)
Th
Families and Genera of Vascular Plants 4, pp. 711. Berlin:
Springe
Engler A (1905) Araceae Pothoideae. In: Engler A (ed.) D
Pflanzenreich 4, 23B, pp. 308313. Leipzig: W Englemann.
Grayum MH (1987) A summary of evidence and arguments
supportin
the removal ofAcorus from the Araceae. Taxon 36: 723729.
Mayo SJ, Bogner J and Boyce PC (1997) The Genera of Araceae.
Roy
Botanical Gardens, Kew, London.Petersen G (1989) Cytology and
systematics of Araceae. Nordic Journ
of Botany 9: 119166.
Acorales (Sweet Flag)
2 ENCYCLOPEDIA OF LIFE SCIENCES / & 2002 Macmillan
Publishers Ltd, Nature Publishing Group / www.els.net
