Lilioid monocot
Encyclopedia
Lilioid monocots or lilioids is an informal name used for a grade of five monocot order
s (Petrosaviales, Dioscoreales
, Pandanales
, Liliales
and Asparagales
) in which the majority of species have flowers with relatively large, coloured tepal
s, broadly similar to those of lilies
. Another name for this group is petaloid monocots, because the flowers have tepals which all resemble petals. In older classification systems, still found in many books and other sources, many of the species in this group of plants were put into a very broadly defined family Liliaceae (lily family).
of the monocots in which the bracket marks the lilioid monocots, namely the orders Petrosaviales, Dioscoreales
, Pandanales
, Liliales
and Asparagales
. The lilioid monocots all have flowers which can be considered to have been derived from a lily-like flower with six relatively similar tepals, six stamens, and a superior ovary composed of three carpels, with nectaries at the base. This pattern is primitive (plesiomorphic) for the lilioid monocots. Various trends are apparent among the lilioids, e.g. a change to an inferior ovary and a reduction of the number of stamens to three. In some groups (e.g. the genus Trillium
in the Liliales), the tepals are clearly differentiated, so that the flower has three coloured petals and three smaller green sepals. Almost all lilioid monocots retain at least three petal-like tepals.
The orders which evolved before the lilioid monocots, the Acorales and Alismatales, have flowers which differ in several ways. Some, like Acorus
, have insignificant flowers. Others, like Butomus
, have flowers with six coloured tepals, and so could be called 'petaloid'; however, the number of stamens and carpels is greater than in the lilioid monocots.
The later evolved commelinids have various kinds of flower, few of which are 'lily-like'. In the order Poales (grasses, rushes and sedges), flowers are either petal-less or have small, unshowy petals. Many species in the order Zingiberales have brightly coloured and very showy flowers. However, these are often deceptive. For example, the six tepals of canna
s are small and hidden under expanded and brightly coloured stamen
s or staminode
s, which look like petals, but are not. However, some commelinids (e.g. Tradescantia
) do have petaloid flowers, so the term 'lilioid' is a more accurate one for the group which excludes them.
.) With the advent of DNA sequencing
and the use of genetic data in determining relationships between species, what many taxonomists had long suspected was confirmed: the old Liliaceae family was highly polyphyletic, comprising a significant number of unrelated groups, which are now placed in quite separate families – and indeed orders, since some genera which were in the old Liliaceae are now placed in different families in the order Asparagales (e.g. Hyacinthus is now in the family Asparagaceae
).
The full extent of the changes required to traditional classification systems only become apparent in the 1990s; the system produced by the Angiosperm Phylogeny Group
in 1998
represented one of the first attempts at a classification which took into account genetic evidence. Textbooks and other sources produced in the last century are inevitably based on older classifications. Publications using versions of the APG system are now beginning to appear and the influential World Checklist of Selected Plant Families from the Royal Botanic Gardens, Kew
is being updated to the APG III system
and hence the classification of the lilioid monocots shown in the cladogram above.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
s (Petrosaviales, Dioscoreales
Dioscoreales
Dioscoreales is a botanical name for an order of flowering plants. Of necessity it contains the family Dioscoreaceae.In the APG II system, of 2003, this order was placed in the clade monocots and comprised the families Burmanniaceae, Dioscoreaceae and Nartheciaceae.Under the APG system of 1998,...
, Pandanales
Pandanales
Pandanales is an order of flowering plants, with a pantropical distribution.The APG III system places the Pandanales in the monocots. Both the APG III and APG II systems include five families in this order:* Cyclanthaceae* Pandanaceae* Stemonaceae...
, Liliales
Liliales
Liliales is an order of monocotyledonous flowering plants. This order of necessity includes the family Liliaceae, but both the family and the order have had a widely disputed history, with the circumscription varying greatly from one taxonomist to another...
and Asparagales
Asparagales
Asparagales is the name of an order of plants, used in modern classification systems such as the APG III system . The order takes its name from the family Asparagaceae and is placed in the monocots. The order has only recently been recognized in classification systems...
) in which the majority of species have flowers with relatively large, coloured tepal
Tepal
Tepals are elements of the perianth, or outer part of a flower, which include the petals or sepals. The term tepal is more often applied specifically when all segments of the perianth are of similar shape and color, or undifferentiated, which is called perigone...
s, broadly similar to those of lilies
Lilium
Lilium is a genus of herbaceous flowering plants growing from bulbs. Most species are native to the temperate northern hemisphere, though the range extends into the northern subtropics...
. Another name for this group is petaloid monocots, because the flowers have tepals which all resemble petals. In older classification systems, still found in many books and other sources, many of the species in this group of plants were put into a very broadly defined family Liliaceae (lily family).
Flowers
The diagram shows a cladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
of the monocots in which the bracket marks the lilioid monocots, namely the orders Petrosaviales, Dioscoreales
Dioscoreales
Dioscoreales is a botanical name for an order of flowering plants. Of necessity it contains the family Dioscoreaceae.In the APG II system, of 2003, this order was placed in the clade monocots and comprised the families Burmanniaceae, Dioscoreaceae and Nartheciaceae.Under the APG system of 1998,...
, Pandanales
Pandanales
Pandanales is an order of flowering plants, with a pantropical distribution.The APG III system places the Pandanales in the monocots. Both the APG III and APG II systems include five families in this order:* Cyclanthaceae* Pandanaceae* Stemonaceae...
, Liliales
Liliales
Liliales is an order of monocotyledonous flowering plants. This order of necessity includes the family Liliaceae, but both the family and the order have had a widely disputed history, with the circumscription varying greatly from one taxonomist to another...
and Asparagales
Asparagales
Asparagales is the name of an order of plants, used in modern classification systems such as the APG III system . The order takes its name from the family Asparagaceae and is placed in the monocots. The order has only recently been recognized in classification systems...
. The lilioid monocots all have flowers which can be considered to have been derived from a lily-like flower with six relatively similar tepals, six stamens, and a superior ovary composed of three carpels, with nectaries at the base. This pattern is primitive (plesiomorphic) for the lilioid monocots. Various trends are apparent among the lilioids, e.g. a change to an inferior ovary and a reduction of the number of stamens to three. In some groups (e.g. the genus Trillium
Trillium
Trillium is a genus of about 40–50 species of spring ephemeral perennials, native to temperate regions of North America and Asia....
in the Liliales), the tepals are clearly differentiated, so that the flower has three coloured petals and three smaller green sepals. Almost all lilioid monocots retain at least three petal-like tepals.
Acorus
Acorus is a genus of monocot flowering plants. This genus was once placed within the family Araceae , but more recent classifications place it in its own family Acoraceae and order Acorales, of which it is the sole genus of the oldest surviving line of monocots. The exact relationship of Acorus to...
, have insignificant flowers. Others, like Butomus
Butomus
Butomus is the sole genus in the monogeneric plant family Butomaceae, containing the single species Butomus umbellatus, also known as flowering rush or grass rush.-Description:...
, have flowers with six coloured tepals, and so could be called 'petaloid'; however, the number of stamens and carpels is greater than in the lilioid monocots.
The later evolved commelinids have various kinds of flower, few of which are 'lily-like'. In the order Poales (grasses, rushes and sedges), flowers are either petal-less or have small, unshowy petals. Many species in the order Zingiberales have brightly coloured and very showy flowers. However, these are often deceptive. For example, the six tepals of canna
Canna (plant)
Canna is a genus of nineteen species of flowering plants. The closest living relations to cannas are the other plant families of the order Zingiberales, that is the gingers, bananas, marantas, heliconias, strelitzias, etc.Canna is the only genus in the family Cannaceae...
s are small and hidden under expanded and brightly coloured stamen
Stamen
The stamen is the pollen producing reproductive organ of a flower...
s or staminode
Staminode
In botany, a staminode is an often rudimentary, sterile or abortive stamen. This means that it does not produce pollen. Staminodes are frequently inconspicuous and stamen-like, usually occurring at the inner whorl of the flower, but are also sometimes long enough to protrude from the...
s, which look like petals, but are not. However, some commelinids (e.g. Tradescantia
Tradescantia
Tradescantia , the Spiderworts, is a genus of an estimated 71 species of perennial plants in the family Commelinaceae, native to the New World from southern Canada south to northern Argentina. They are weakly upright to scrambling plants, growing to 30–60 cm tall, and are commonly found...
) do have petaloid flowers, so the term 'lilioid' is a more accurate one for the group which excludes them.
The lilioids and classification systems
When classification systems were based on morphological characters, lilioid species which clearly departed from the 'lily' pattern were easily placed into separate families. For example, the Amaryllidaceae contained species whose flowers had six stamens and an inferior ovary. The Iridaceae contained those with three stamens and an inferior ovary. The 'left-overs' were put together in a very broadly defined Liliaceae. (See, for example, the Cronquist systemCronquist system
The Cronquist system is a taxonomic classification system of flowering plants. It was developed by Arthur Cronquist in his texts An Integrated System of Classification of Flowering Plants and The Evolution and Classification of Flowering Plants .Cronquist's system places flowering plants into two...
.) With the advent of DNA sequencing
DNA sequencing
DNA sequencing includes several methods and technologies that are used for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....
and the use of genetic data in determining relationships between species, what many taxonomists had long suspected was confirmed: the old Liliaceae family was highly polyphyletic, comprising a significant number of unrelated groups, which are now placed in quite separate families – and indeed orders, since some genera which were in the old Liliaceae are now placed in different families in the order Asparagales (e.g. Hyacinthus is now in the family Asparagaceae
Asparagaceae
Asparagaceae is the botanical name of a family of flowering plants, placed in the order Asparagales of the monocots.In earlier classification systems, the species involved were often treated as belonging to the family Liliaceae...
).
The full extent of the changes required to traditional classification systems only become apparent in the 1990s; the system produced by the Angiosperm Phylogeny Group
Angiosperm Phylogeny Group
The Angiosperm Phylogeny Group, or APG, refers to an informal international group of systematic botanists who came together to try to establish a consensus on the taxonomy of flowering plants that would reflect new knowledge about plant relationships discovered through phylogenetic studies., three...
in 1998
APG system
The APG system of plant classification is the first, now obsolete, version of a modern, mostly molecular-based, system of plant taxonomy that was published in 1998 by the Angiosperm Phylogeny Group. It was superseded in 2003 by a revision, the APG II system, and then in 2009 by a further...
represented one of the first attempts at a classification which took into account genetic evidence. Textbooks and other sources produced in the last century are inevitably based on older classifications. Publications using versions of the APG system are now beginning to appear and the influential World Checklist of Selected Plant Families from the Royal Botanic Gardens, Kew
Royal Botanic Gardens, Kew
The Royal Botanic Gardens, Kew, usually referred to as Kew Gardens, is 121 hectares of gardens and botanical glasshouses between Richmond and Kew in southwest London, England. "The Royal Botanic Gardens, Kew" and the brand name "Kew" are also used as umbrella terms for the institution that runs...
is being updated to the APG III system
APG III system
The APG III system of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy...
and hence the classification of the lilioid monocots shown in the cladogram above.