structure and life cycle of Anthoceros

1. ANTHOCEROS (Hornwort)
Division: Bryophyta, Class: Anthoceratopsida Order: Anthocerotales Family: Anthocerotaceae
Anthoceratopsida, Anthocerotaceae,
Genus: Anthoceros
Morphology of thallus:
• Adult plant represents the gametophytic generation. It is thalloid, dorsiventrally flattened, green,
irregularly lobed or radially dissected structure
structure.
• Definite midrib and dichotomous branching is absent.
• Dorsal surface is smooth, velvety or rough.
• On the ventral surface, many s smooth walled rhizoids are
present which help in fixation. Scales and tuberculate rhizoids
are absent. Some bluish mucilaginous spots are also seen
which represent the colonies of blue
blue-green alga (Nostoc or
Anabaena).
• At the end of the rainy season, elonga
elongated horn- like sporophytes are seen on the gametophyte.
Anatomy of thallus:
• Internally, the thallus is few cells in thickness and is homogeneous without any tissue
differentiation and cell specialisation. It consists of parenchymatous tissue covered by single
layer each of upper and lower epidermis.
• Each parenchyma cell has a distinct
nucleus, large chloroplast and a single
pyrenoid.
• Smooth-walled rhizoids arise from the
lower epidermal cells, in the middle region
of ventral surface.
• On the ventral side, mucilage filled
cavities are present which open outside by
h
slime pores. Endophytic algae such as
Nostoc, Anabaena, etc. are present in
re
these mucilage cavities.
Reproduction:
a) Vegetative methods:
1. Fragmentation:
2. Gemmae: Formation of gemmae is reported on the thallus of some
:
species such as A. Glandulosus
Glandulosus.
3. Tubers: Corky tubers develop on the margins of thallus, usually
:
during dry and unfavourable conditions. Each tuber develops into a
new plant with the return of favour
favourable conditions.
4. Persistent apices:
b) Sexual Reproduction:

2. Sexual reproduction is oogamous type. Many species are monoecious while some are
dioecious. In monoecious species, antheridia develop much earlier to archegonia (Protandrous
condition). Sex organs develop inside the gametophytic
thallus.
Structure of Antheridia:
• Develop singly or in groups, in the upper region of
the thallus, inside closed cavities called antheridial
chambers.
• Each antheridium has an ovoid body and a
multicellular, slender stalk. The body is covered by
a single layered antheridial wall.
• Inside the body, a mass of androcytes or
spermatocytes are present. Each spermatocyte is a
bi-flagellate ‘coma’ shaped structure with a single
haploid nucleus.
Structure of Archegonia:
• They are present sunken in the thallus on the upper side,
close to the apex, in acropetal order.
• Each archegonium is flask-like in appearance with a basal
swollen venter region and a narrow neck.
• The venter has a basal egg cell and an upper venter canal cell.
4-6 neck canal cells are arranged in a row at the neck part.
• There is no jacket cells covering the archegonium. The
vegetative cells of the thallus provide protection to the
archegonium. Cover cells or lid cells are found at the tip of the archegonium.
Fertilisation: Rain splash mechanism, as in Riccia/Marchantia.
Structure of Sporophyte:
The diploid zygote develops into a sporophyte on the upper surface of the gametophyte.
Mature sporophytes are elongated (2-3 cm long), horn-like
structures with a bulbous base. It is covered at the base by a
tubular involucre which is developed from the gametophytic
tissue.
The sporophyte is differentiated into 3 distinct regions:
1. Foot: It is the basal, bulbous structure which is found deeply
embedded in the gametophytic tissue. It helps in attaching the
sporophyte to gametophyte and in absorption of water and
nutrients from it. Foot is made up of parenchyma cells.
2. Intermediate or intercalary zone: It is a narrow zone of
meristematic cells located between the basal foot and the upper capsule. These cells help in
the continuous growth of the sporophyte.
3. Capsule: It is the fertile, major and conspicuous part of the sporophyte which is long and
cylindrical. It is green when young, but turns grey or brown on maturity. The capsule is
composed of the following structures:
a) Columella: It is the central solid core of sterile cells, consisting of 16 vertical rows of cells. It
extends from the base to almost to the tip of the capsule.

3. b)Sporogenous tissue: It is
the mass of fertile spore-
forming cells surrounding the
columella, like a dome. At
the base of the capsule, it is
single layered and called
archesporium. It becomes 2-
4 layered and develops into
diploid spore mother cells
upwards. Towards the tip of
the capsule, the spore
mother cells divide by
meiosis and produce haploid
spores. Along with spores,
chains of sterile cells called
pseudo-elaters are also
present. They are without
spiral thickenings and are
nutritive in function.
c) Capsule wall: It is the
outer wall of the capsule
which is 4-6 layers in
thickness. The outermost
layer is called epidermis
which is interrupted by
stomata. The inner layers
consist of chlorenchymatous
cells and are
photosynthetic. Therefore,
the sporophyte of anthoceros is partially autotrophic or semi-independent.
Dehiscence of Sporophyte and germination of spores:
The spores ripen and mature basipetally, from top downwards. The mature part looses water,
shrinks and ruptures or splits longitudinally, exposing the spores. The splits extend downwards. The
exposed spores are blown away by the wind.
The dispersed spores germinate during the next moist season. During germination, they
absorb water and swell. The exospore ruptures and the endospore comes out in the form of a
germinal tube. The tip of the germinal tube divides repeatedly forming a young thallus.
©Dr. M. Jayakara Bhandary
Associate Professor of Botany
Government College, Karwar