Equisetidae

See Pteridophyta for an introduction to seedless vascular plants

The horsetails, called Equisetidae in the modern classification by Christenhusz et al. 2011, or also Equisetopsida or Equisetophyta, and in paleobotany it is more common Sphenopsida, are vascular plants related to ferns that appeared in Devonian, but currently only the genus Equisetum survives, although there are representatives of extinct orders. This group is monophyletic, even with its extinct representatives, due to its distinctive morphology. They are small plants, although in the past a variety of calamitaceae reached 15 meters during the Permian.

Phylogeny

Theoretical Introduction in Philogenia

Molecular and genetic analyzes of phylogeny can only be done on living representatives, as circumscribed by Smith et al. (2006) (see factsheet), at least Equisetales is monophyletic (Pryer et al. 2001a and 2004b, Des Marais et al. 2003, Guillon 2004), but due to Due to the unique architecture of the sporophyte stem, it is very likely that all the fossils found belong to this clade.

This clade clearly belongs to the Monilophytes (Pryer et al. 2001), although its relationship to the rest of the Monilophyte branches is still unclear. Some studies based on plastid DNA place the subclass as sister to the Marattiidae (Pryer et al. 2004, Smith et al. 2006a), but Rai & Graham (2010) found it sister to the rest of the ferns. This relationship is more in line with the fossil record (Taylor et al. 2009) and agrees with the morphology of the group, although Christenhusz et al. 2011 think horsetails are best placed in the lineage of ferns—Polypodiopsida (as in Pryer et al. 2001).

Ecology and evolution

Fossil Equiset Sphenophyllum.

This class is well known from the fossil record, as it is easily identified due to its characteristic stem architecture.

Like the lycophytes, they already existed in the Devonian, but they became much more abundant in the Carboniferous, at which time some of them had much larger leaves, developed heterospory, and became impressive trees.

The genus Calamites produced large trees up to 18 meters tall with trunks up to 50 centimeters in diameter.

Equisetum is very similar to Equisetites from 300 million years ago.

The approximate relationships between groups are as follows:

Taxonomy

Theoretical Introduction in Taxonomy

Synonymy

The group of Equisetae that includes even those extinct has been named Equisetales (de Candolle 1813), Equisetopsida (Agardh 1825, AR Smith et al 2006), Equisetinae (Eichler 1883, Engler 1886, Wettstein 1924), Sphenopsida (Engler 1924, Whittaker & Margulis 1978), Equisetaceae (Willkomm 1854), Calamophyta (Haeckel 1866, Bessey 1907, Barkley 1949, GM Smith 1955), Equisetophyta (Takhtajan 1964, Cronquist et al 1966), Equisetatae (Kubitski 1990), Sphenophyta (Margulis & Chapman 2009) and Equisetidae (Warming 1883, Chase & Reveal 2009, Christenhusz et al 2011, Ruggiero et al 2015).

The term Equisetopsida according to Chase & Reveal 2009 is equivalent to Embryophyta.

Christenhusz et al. 2011

The most up-to-date classification of the living members of the pteridophyte genus is that of Christenhusz et al. 2011 (based on Smith et al. 2006, 2008); which also provides a linear sequence of the lycophytes and monilophytes.

• Sub-class: II Equisetidae Warm, Osnov. Bot.: 221 (1883).
  • Order D. Equisets DC. ex Bercht. & J.Presl, Přir. Rostlin: 271 (1820). 1 family.
    • Family 4. Equisetaceae Michx. ex DC., Essai Propr. Get in. Pl.: 49 (1804).

1 gender (Equisetum). References: Des Marais et al. (2003), Guillon (2004, 2007), Hauke (1963, 1978), Schaffner (1930).

Classification sensu Smith et al. 2006

Clades and higher taxa: Plantae (clade), Viridiplantae, Streptophyta, Streptophytina, Embryophyta, Tracheophyta, Euphyllophyta, Monilophyta, Class Equisetopsida.

Synonyms: Sphenopsida, "horsetails" in English

Circumscription: A single living order:

• Equisetales, with a family Equisetaceae, and a genus Equisetum, about 15 living species.

Fossil orders

• Pseudobornials
• Sphenophyllales
• Calamitales

Sterilized vegetative stems Equisetum telmateia.

Other classifications

Traditional classifications such as Engler's placed the equisetopsids in their own class within the pteridophytes or seedless vascular plants, that is, it was accepted that they were not bryophytes and that they were not seed-bearing vascular plants either. Due to the distinctive characteristics of the stem, they were separated from the ferns with conspicuous megaphylls (Pterophyta, Pteropsida or Filicopsida sensu Engler), and also separated from the Psilotaceae and the Lycophytes, groups that despite having reduced leaves did not seem to be related to them. the equisetopsids. The sensu Engler classification is as follows:

• Plant Kingdom (poliphytic), Embryophyta asyphonogama (paraphytic), Pteridophyta subdivision (paraphylatic), class Sphenopsida (monophylaxis, equivalent to Equisetopsida sensu Smith et al.).

Characters

Figure 2. Schematic diagram of the life cycle of vascular plants without seed.

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References:
n : haploid generation,
2n : diploid generation,
m! : mitosis,
M! : meiosis,
F! : fertilization

Equisetopsids are vascular plants with a haplodiplonte life cycle where the alternation of generations is well manifested, with multicellular and independent sporophyte and gametophyte, with spores as the dispersal and resistance unit. The gametophyte is a "tallus" (body without organization), and the sporophyte is a "corm" (with root, stem and vascular system). Due to these characteristics, they are traditionally grouped with the "pteridophytes".

They have sporophytes with megaphylls or "fronds" (Euphyllophyta), which in Equisetum are reduced (which is why he prefers to call them "reduced euphylls" to avoid calling them "megaphylls"). Some authors still call them "microphiles" due to its small size, but the tendency is to use that term only to refer to the microphylls of the lycophytes, of a different phylogenetic origin. Other authors call the leaves "scales", especially in English translations, that term gives priority to the texture of the leaves, but that term can be confusing (if necessary it could be translated as "scaly leaves").

Although not obvious, there are morphological characters that support the inclusion of Equisetum in the Monilophyta clade, for example the morphology of spermatozoa (Renzaglia et al. 2000) and root characters (Kato 1983).

Their general appearance is vaguely reminiscent of bamboo (with which they have no relationship).

Equisetopsids have hollow, jointed stems with clearly marked nodes, and branches arranged in whorls around the stem. The internodes of the stem are grooved forming ridges and valleys, the epidermal cells of the ridges ("ridges") deposit silica on the surface that acts as a supporting reinforcement.

The leaves are born at the nodes, forming connate whorls at their base. The leaves, although they are euphyllous, are small, scaly.

The sporangia where the spores originate are born in modified leaves, without chlorophyll, non-photosynthetic, with a foot, called sporangiophores. The sporangia are located on the ventral side of the sporangiophore, towards the stem side. The sporangiophores are all located together in the apical part of the stem, forming what is known as "strobili".

Modern horsetail plants are homosporic plants (all spores are the same). In homosporic plants in general, the spores have the ability to produce gametophytes capable of giving rise to male and female gametes (the spores produce hermaphroditic gametophytes). However, there is controversy about whether the equisetopsid gametophytes are hermaphrodites or not. Some gametophytes produce only antheridia (giving male gametes), other gametophytes produce only archegonia (giving female gametes). According to Judd et al. (2002), at least the "female" they become bisexual later.

For a more detailed description and photos see horsetail.