Complex thalloids
Much work remains to resolve relationships among taxa in this group. Forrest et al. (2006) were able, however to pinpoint or confirm several important dichotomies in this lineage.
| Figure 5. Marchantiopsida (based on the topology from a 5 partition Bayesian analysis of 5 loci including chloroplast, nuclear, and mitochondrial DNA). Numbers above the branches are Maximum Parsimony bootstrap values/homogeneous Bayesian posterior probabilities (PPs)/5-partition Bayesian PPs/14-partition Bayesian PPs. |
Figure 5 (Forrest et al., 2006) shows these established dichotomies. The Blasiales (or Blasiaceae) are the earliest branching lineage. This family was an unexpected member of the complex thalloid clade. It was formerly placed within the simple thalloids (see Classification) based on its morphological characteristics (e.g., a unistratose thallus with simple, cylindrical capsules), however, several characteristics have been noted that it shares with the Marchantiopsida (or at least some members of the Marchantiopsida; Forrest et al., 2006):
- Gemmae in receptacles on thallus surface
- Ventral scales
- True calyptra
- Cuneate apical cells
The earliest branch of the “true” complex thalloids is Neohodgsonia. This genus has unique, branching gametangiophores. It is a member of the Marchantiales, a clearly paraphyletic group. The Sphaerocarales have a unique set of characteristics, including a unistratose thallus, flask-like involucres enclosing their gametangia, and the lack of ventral scales or pegged rhizoids.
Branched archegoniophore of Neohodgsonia; dried herbarium specimen (photo by B. Shaw) |
Sphaerocarpos texanus (photo by B. Shaw) |
The Monocleales, previously thought to be a “primitive” group, perhaps representing the link between the complex thalloids and simple thalloids, is well-nested within the clade. Monoclea, lacking ventral scales or pegged rhizoids and possessing a cylindrical capsule on an elongated seta, is sister to Dumortiera, a genus possessing most of the common characteristics associated with the Marchantiopsida (see Morphological Diversity). However, several features do unite the two (Forrest et al., 2006):
- Sessile rounded male receptacles
- Lack of air chambers
- Monoplastidic meiosis
- Slightly lobed sporocytes
The Ricciales, whose members have very reduced gametangia and sporophytes, are also well nested within the Marchantiopsida clade. The remaining Marchantialean groups are those with mostly “typical” morphology (see Morphological Diversity). Examples of these typical complex thalloids are Marchantia and Asterella, shown below.
Marchantia with archegoniophores and antheridiophores
(photo by J. Shaw) |
Archegoniophores on Asterella (photo by L. Zhang) |
Haplomitriaceae and Treubiaceae
Complex Thalloids and the Blasiaceae
Simple thalloids I
Simple thalloids II plus the Pleuroziaceae
Leafy I
Leafy II
.gif){kind=logo}