Lilioid monocots

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Lilioid monocots
Flowers of Lilium candidum
Lilium candidum
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Grade: Lilioid monocots
Orders
  • Takht.
    (1997)
  • R.Br.
    (1835)
  • J.Presl
    (1820)
  • Perleb
    (1826)
  • Asparagales Link 1829

Lilioid monocots (lilioids, liliid monocots, petaloid monocots, petaloid lilioid monocots) is an informal name used for a

sensu lato or s.l. (lily family). These classification systems are still found in many books and other sources. Within the monocots the Liliaceae s.l. were distinguished from the Glumaceae
.

The development of

paraphyletic in the sense that commelinids form a sister group
to Asparagales.

Description

True lilioids

The descriptive term "petaloid lilioid monocot" relates to the conspicuous petal-like (

stamens. The typical lilioid gynoecium
has three carpels fused into a superior trilocular (three-chambered)
nectaries at the base.[3]

However, floral

Various trends are apparent among the lilioids, notably a change to an

inferior ovary and a reduction of the number of stamens to three. In some groups (such as the genus Trillium in the Liliaceae), the tepals have become 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.[5] Since some commelinids (e.g., Palisota in the Commelinaceae, Haemodoraceae, Philydraceae, and Pontederiaceae) have petaloid flowers, the term 'lilioid' is a more accurate one for the group which excludes them, since the term petaloid monocot is still occasionally used in describing commelinids. The morphological concept of petaloid monocots has been equated with "animal-attracting" (that is, for pollination) as opposed to wind-pollinating plants (such as grasses) that have evolved very different floral structures.[6] Pollen structure shows that of the two main tapetum types, secretory and plasmodial, the lilioid monocots are nearly all secretory.[7]

Lilioid monocots: Botanical illustrations of
Asparagus officinalis

Comparison with other monocot orders

In the orders that branched off before the lilioid monocots, the

Acorales and Alismatales, flowers differ in several ways. In some cases, like Acorus (Acorales), they have become insignificant. In others, like Butomus
(Alismatales), they have six coloured tepals, and so could be called 'petaloid', but stamens and carpels are more numerous than in the lilioid monocots.

The later evolved commelinids have various kinds of flower, few of which are 'lily-like'. In the order Poales, comprising grasses, rushes and sedges, flowers are either petal-less or have small, unshowy petals. Many Zingiberales species have brightly coloured and showy flowers. However, their apparent structure is misleading. For example, the six tepals of cannas are small and hidden under expanded and brightly coloured stamens or staminodes which resemble petals and may be mistaken for them.[8]

Taxonomy

Early history

Xanthorrhaea hastilis, John Lindley: Vegetable Kingdom, 1846

In one of the earliest monocot taxonomies, that of

Bentham and Hooker's Coronarieæ and Hutchinson's Corolliferae ("Corolla bearing") (1936).[10] Hence the concept that there was a natural grouping of monocots whose flowers were predominantly petaloid, gave notion to the term "petaloid monocots".[11]
The core group of petaloids were the Liliaceae, hence "lilioid monocots".

The term "lilioid monocot" or lilioid" has had widely varying interpretations.

superorder Lilianae, the whole of Liliales, or restricted to Cronquist's broadly defined Liliaceae. Although "petaloid" and "lilioid" have often been used interchangeably, as Heywood points out, some usages of "petaloid monocot", particularly in horticulture, are so broad as to be almost meaningless in that it had been used to refer to all species with conspicuous petals or perianth segments (tepals), which would cover a broad swathe of families (he estimated three dozen across many orders).[11] Other authors have defined it equally broadly as "having two whorls of tepals (sepals and petals) that are petal-like".[8]

As Kron and

geophytes, as constituting the lilioid monocots.[18][17][a]

The development of

synapomorphy, that of a petaloid perianth,[24] yet in discussing his Lilliflorae admitted it was undoubtedly paraphyletic.[b] Dahlgren treated the monocots as split between ten superorders and placed five orders (Dioscoreales, Asparagales, Liliales, Melanthiales, Burmanniales and Orchidales) in his Liliiflorae.[26]

Phylogenetic era

In the 1995 study by Chase et al. referred to above, which was the largest yet to use purely molecular data, the results demonstrated paraphyly of the lilioids. However, because their data contradicted purely morphological phylogenies they were reluctant to draw definite conclusions as to the monophyly of this group.

commelinoids. They based the names of these groups on the closest corresponding superorders and orders of Dahlgren, with the exception of stemonoids (based on Stemonaceae
for which there was no obvious equivalent).

There was no clear clade corresponding to Dahlgren's Liliiflorae, whose families were distributed amongst the aroids and dioscoreoids. Of Dahlgren's Liliiflorae, the Dioscoreales largely grouped into dioscoreoids, with the exception of Stemonaceae. The Asparagales formed two major groupings, which they labelled "higher" and "lower asparagoids", and included both the Iridaceae and Orchidaceae from Dahlgren's Liliales. On the other hand, a number of families from three other orders (Asparagales, Dioscoreales, Melanthiales) segregated together with the remaining Liliales families. Genera from Dahlgren's Melanthiales were found in both dioscoreoids and the redefined Liliales. Finally Dahlgren's Burmanniales were found to belong with the dioscoreoids. Some Asparagales taxa were also found amongst the commelinoids. The stemonoids were formed from Stemonaceae and other families from a variety of orders, including Pandanaceae (which alone formed Dahlgren's Pandaniflorae).

In an attempt to resolve the apparent differences between morphological and molecularly defined trees, a combined analysis was undertaken[c] which confirmed superorder Liliiflorae as monophyletic, provided that a few modifications were undertaken. These included the removal of two tribes of Melanthiaceae (Melanthiales) and the inclusion of three additional families (Cyclanthaceae, Pandanaceae and Velloziaceae) from other superorders. This newly and more narrowly redefined Lilianae/Liliiflorae contained three orders, Asparagales, Liliales and Dioscoreales (which now included the stemonoids). This analysis also allowed for the establishment of a single synapomorphy, although this time by the presence of an inferior ovary. Significantly, the authors noted that it was no wonder the authors of angiosperm classifications had been exasperated by the Lilianae.[27]

Angiosperm Phylogeny Group

These findings, presented at the first Monocot Conference in 1993,[28] with the addition of several studies that had become available in the interim, formed the basis of the 1998 consensus Angiosperm Phylogeny Group (APG) ordinal scheme. Among other things, the Alismatales were expanded and new orders such as Acorales (a placement for Acorus) and Pandanales (which now represented the stemonoids as well as new families) added. While not formally assigning any supraordinal ranks, the classification did recognize an informal grouping of monocot orders as the commelinoids. Otherwise the APG recognized only six monocot orders (Acorales, Alismatales, Asparagales, Dioscoreales, Liliales and Pandanales). The last four were however grouped together in the resulting cladogram and most closely represent the concept of lilioids, although this left some unplaced monocot families, including Corsiaceae and Petrosaviaceae.[29]

Simultaneous with the release of the 1998 APG classification were two events: the publication of Kubitzki's major monograph on the monocots[30] and the Second Monocot Conference. Kubitzki defined superorder Lilianae as all monocots except superorders Commelinae, Alismatanae and the Acoraceae, that is the four orders Asparagales, Liliales, Dioscoreales and Pandanales.[31] The Monocot Conference devoted an entire section to Systematics of the Lilioids[32] and included an update of their previous research by Chase and colleagues.[33] On this occasion the latter felt that there was now enough data to put forward a definitive classification, defining the Lilioids as comprising the four orders placed in Lilianae by Kubitzki. Rudall and colleagues (2002) followed Chase (2000), in using the term "lilioid monocots" and again noting unresolved polytomy between these four orders and the remaining monocot clades (commelinids and Petrosaviaceae), although at that time the Petrosaviaceae were still unplaced.[7][34]

There was now enough new data to justify revising the APG system, and a new classification was issued in 2003. Although this resulted in changes within the orders, it did not affect the relationship between them. Lilioid monocots were discussed but not formally recognized (commelinids, renamed from commelinoids, being the only supraordinal grouping in the monocots to be named) and Petrosaviaceae remained unplaced.

sister clades.[39] Rapid advances in understanding monocot relationships necessitated the release of another revision of the APG classification (2009), which incorporated these advances.[22] Further definition of the relationships between lineages using multiple markers is continuing.[40][41]

Textbooks and other sources produced in the last century are inevitably based on older classifications. Publications using versions of the APG system are now appearing and the

Judd in his Plant systematics.[45]

Phylogeny and evolution

The

mya (million years ago).[41]

Lilianae sensu Chase & Reveal (monocots) 131[46]
          

Acorales

Alismatales

122
          

Petrosaviales

120

Liliales 121

121

Asparagales 120

commelinids 118
          

Dasypogonaceae

Arecales

Poales

          

Zingiberales

Commelinales

Lilioid monocots 122

While this is the most commonly understood relationship, Davis et al. (2013) using a combination of

mitochondrial and plastid genes together with nuclear phytochrome C was in agreement with the earlier APG relationships.[41]

Subdivision

Five orders make up the lilioid monocots.

Japonolirion osense

Petrosaviales

Petrosaviales are a very small order (1 family, 2 genera, about 5 species) of rare leafless achlorophyllous,

monosulcate pollen, and follicular fruit.[49]

Dioscorea balcanica vines growing in Berlin botanical gardens
Dioscorea balcanica

Dioscoreales (yams)

Dioscoreales are a small order (3 families, 21 genera, about 1,000 species) of mainly

contraceptives. They form a sister group to the Pandanales.[50]

Pandanus montanus tree on Reunion Island
Pandanus montanus

Pandanales (pandans)

Pandanales are a medium size order (5 families, 36 genera, about 1,300 species) mainly tropical order many species of which produce strap-like leaves used in the manufacture of baskets, mats and straw hats. The order is very diverse including trees, vines and forest floor saprophytes. They are a sister group to the Dioscoreales.[51]

Flowers of Lilium michiganense
Lilium michiganense

Liliales (lilies)

Liliales are a large size order (10 families, 67 genera, about 1,500 species) distributed worldwide, particularly in subtropical and

pharmaceuticals.[52]

Nolina recurvata

Asparagales (includes orchids, irises, agaves, amaryllis, and onions)

Asparagales are a large very diverse order (14 families, 1,122 genera, about 36,000 species), including many geophytes,

ornamental flowers, vegetables, and spices. Most are herbaceous perennials, but some are trees and climbers.[53]

See also

Notes

  1. ^ Dahlgren did not actually use the exact term.
  2. ^ "This superorder is extraordinarily variable and contains some groups which, in our estimation, are likely to have retained many features from the ancestral monocotyledons. The wide range of variation makes a definition difficult and in an evolutionary sense this unit is undoubtedly paraphyletic rather than monophyletic "(emphasis added).[25]
  3. ^ Subsequent to the 1993 Monocot Conference, and prior to publication.

References

Bibliography

Books
Symposia
Chapters
Articles
APG
Websites