Anthocerotophyta
Anthocerotophyta (an-tha-se-ro-TA-fa-ta) is made of three Greek roots that mean flower (anthos -άνθος); horn (keras -κέρας); and plant (phyto -φυτό). The reference is to the horn-like sporangium or fruiting body. The phylum name is formalized from a common genus, Anthoceros. INTRODUCTION TO THE ANTHOCEROTOPHYTA
The hornworts, in the gametophyte stage, resemble the thallose hepatics; however, when grown in uncrowded conditions, the gametophytes tend to be almost circular. The thallus structure of hornworts is simple, much simpler than Marchantia. Typically, they have an epidermis and air chambers. Some taxa enter into a symbiotic relationship with Nostoc, which enters the air chambers through cracks in the ventral surface. In general, the gametophyte has a rather greasy appearance. Another unique feature of this phylum is the occurrence of massive plastids opposed to the small lenticular ones of other embryophytes
They never have gametophores; rather, archegonia and antheridia occur on the upper surface of the thallus (see Figure 1). The archegonia and antheridia, however, are not well differentiated from the thallus (Figure 1-G&H). For example the archegonium is reduced to neck canal cells embedded in undifferentiated thallus tissue. The situation is similar for the antheridia. Despite the apparent simplicity of the gametangia, the sporophyte is quite complex (Figure 1-A-C). The sporophyte emerges by the growth of cells from an intercalary meristem at the top of the foot. The developing capsule appears horn-like with relatively little fertile (or sporogenous) tissue. The sporophyte capsule also has photosynthetic tissue and stomata (Figure 1-B&C). The capsule is somewhat indeterminate with spores at different developmental stages and a continual dehiscence along its longitudinal slits (Figure 1-A,D&E). Spores are shed with the aid of elaters (Figure 1-F).
LEIOSPOROCERTALES (Clade EL)
Gametophytes are thalloid and solid (no internal
The hornworts, in the gametophyte stage, resemble the thallose hepatics; however, when grown in uncrowded conditions, the gametophytes tend to be almost circular. The thallus structure of hornworts is simple, much simpler than Marchantia. Typically, they have an epidermis and air chambers. Some taxa enter into a symbiotic relationship with Nostoc, which enters the air chambers through cracks in the ventral surface. In general, the gametophyte has a rather greasy appearance. Another unique feature of this phylum is the occurrence of massive plastids opposed to the small lenticular ones of other embryophytes
They never have gametophores; rather, archegonia and antheridia occur on the upper surface of the thallus (see Figure 1). The archegonia and antheridia, however, are not well differentiated from the thallus (Figure 1-G&H). For example the archegonium is reduced to neck canal cells embedded in undifferentiated thallus tissue. The situation is similar for the antheridia. Despite the apparent simplicity of the gametangia, the sporophyte is quite complex (Figure 1-A-C). The sporophyte emerges by the growth of cells from an intercalary meristem at the top of the foot. The developing capsule appears horn-like with relatively little fertile (or sporogenous) tissue. The sporophyte capsule also has photosynthetic tissue and stomata (Figure 1-B&C). The capsule is somewhat indeterminate with spores at different developmental stages and a continual dehiscence along its longitudinal slits (Figure 1-A,D&E). Spores are shed with the aid of elaters (Figure 1-F).
LEIOSPOROCERTALES (Clade EL)
Gametophytes are thalloid and solid (no internal