Hamamelidae

Hamamelidae is a taxon of the subclass category, belonging to the dicotyledons, which grouped plants whose main characteristic was that they had wind-pollinated flowers (anemophilous) usually grouped in catkins. The taxon was used by Cronquist and other classification systems for a time (see Cronquist 1981, 1988, Takhtajan 1980 which correctly spells it as Hamamelididae . Numerous lines of evidence show that this taxon is not it is monophyletic.In modern classifications such as the APG III classification system (2009) and the APWeb (2001 onwards), the taxon was abandoned.

History of the taxon

Its historical origins can be traced back to pre-Linnean times, where the existence of a "amentiferous" (also sometimes called Amentiferae, see Stern 1973 for a historical summary), although at the time, before the advent of evolutionary theory, taxa were not thought to reflect of the phylogeny of organisms. Its circumscription (that is, what subtaxa the taxon is composed of) varied with the classification systems, of which the best remembered is Cronquist's (Cronquist 1981, 1988, see circumscription in Taxonomy section). Ultimately, the concept of such a high-ranking taxon of mint plants was abandoned in current classification systems (such as APG, APG II, APG III, APWeb), because no monophyletic taxon has been recovered that responds to their characters.

Description

Theoretical Introduction in Descriptive Terminology of Plants

In this subclass were grouped several families with small flowers and generally without perianth or with an apetalous perianth, pollinated by wind (anemophily), usually grouped in inflorescences called catkins.

Leaves simple or, more rarely, pinnate or palmate. Sepals, when present, usually small and scale-shaped. In the few species that have petals, they are free, small, and generally inconspicuous. Androecium formed by (1)2-several stamens, which can become numerous. The connective may be prolonged, but it is never laminar. Pollen is binucleate or trinucleate and has (2)3-many openings. The gynoecium consists of 1-several carpels that are usually welded into a compound ovary. The seminal primordia can be anatropous or orthotropic, more or less clearly crassinucellate.

Phylogeny

Theoretical Introduction in Philogenia

Numerous lines of evidence show that this subclass is not monophyletic (Thorne 1973a, Donoghue and Doyle 1989, Wolfe 1989, Crane and Blackmore 1989, Hufford and Crane 1989, Hufford 1992, Chase et al. 1993, Manos et al. 1993).

Some families that had been considered hamamelids, such as the Platanaceae, Trochodendraceae, and Buxaceae, are lineages that diverged early from the eudicots. Also related to Platanaceae above all are probably Proteaceae and Nelumbonaceae (the three families today considered Proteales, see APG II classification system). Both morphological and DNA analyzes (in the sequences rbcL, atpB, 18S rDNA) support the location of these families as basal eudicots, and also the formation of the Proteales clade. as formed by Platanaceae + Proteaceae + Nelumbonaceae (APG 1998, 2003, Chase et al. 1993, Hufford 1992, Manos et al. 1993, Soltis < i>et al. 1997, 2000).

Hamamelidaceae and Cercidiphyllaceae in particular have sometimes been considered related to Platanaceae (Hufford and Crane 1989, Schwarzwalder and Dilcher 1991, Hufford 1992), but this placement is not supported by DNA sequence analysis (Chase < i>et al. 1993, Savolainen et al. 2000a, b, Soltis et al. 1997, 2000). DNA evidence supports the Hamamelidaceae and Cercidiphyllaceae as being related to the Saxifragaceae (all three now placed in the order Saxifragales).

Other families of hamamelids with reduced flowers today are placed in Saxifragales, Fagales or Malpighiales.

Taxonomy

Theoretical Introduction in Taxonomy

In modern classifications such as the APG III classification system (2009), the taxon was abandoned, being polyphyletic, placing the families and orders that were recovered as monophyletic in the clade Eudicotyledoneae, where they are located in this way (in in bold the families that belonged to the hamamelids according to Cronquist):

Basal eudicots:

• Ranunculales (Ranunculaceae, Eupteleaceae among others)
• Proteals (Proteaceae, Platanaceae and Nelumbonaceae)
• Trochodendrales (monotypical, Trochodendraceae)
• Buxales (Buxales)Buxaceae, Didymelaceae)

Nucleus of Eudicots (today Gunneridae, named after APG III) neither rosids nor asterids:

• Gunnerales (Gunneraceae and Myrothamnaceae, the order is belonging to the "nucle of eudicothylenes" in APG II and APG III, the APW maintained it outside the core but since 2009 it also includes it in the core)
• Saxifragales (Saxifragaceae, Hamamelidaceae, Cercidiphyllaceae, Daphniphyllaceae among others)

Rosids:

• Fagales (Fagaceae, Betulaceae, Casuarinaceae, Juglandaceae, Myricaceae, Nothofagaceae (in Cronquist included in Fagaceae), Rhoipteleaceae among others)
• Malpighiales (Malpighiaceae, Balanophaceae, Picrodendraceae among others).
• Sapindales (in the family Simaroubaceae is located the only leitnerian, Leitneria floridana)
• Rosales (Rosaceae, all in the old order Urticales sensu Cronquist: Barbeyaceae, Cannabaceae, Urticaceae including Cecropiaceae, Moraceae, Ulmaceaeamong others)

Asterids:

• Garryales (Garryaceae, Eucommiaceae among others)

In Cronquist's (1981, 1988) classification system, the subclass comprised 11 orders, 24 families, and 3,400 species. The sensu Cronquist classification into orders and families can be seen by displaying the box below.