ORDER ANTHOCEROTALES
Anthoceros
They occur in moist and shady places . Plant body is dark green , dorsiventral , lobed and prostate thallus . Thallus is without sharply defined midrib .Ventral surface bears always unicellular smooth walled rhizoids along the median line . Scales and tuberculate rhizoids are absent in anthoceros .The chloroplasts contain many pyrenoids ( characteristic feature ) . Thallus has many mucilaginous cavities which are invaded by Nostoc colonies . The presence of endophytic alga Nostoc in anthoceros is not considered a symbiotic association as anthoceros can grow normally even without mucilaginous cavities . Nostoc lives in anthoceros thallus possibly as space parasite . Mucilaginous cavities open on the ventral surface by slime pores.
The vegetative reproduction in anthoceros occurs by progressive death and decay of thallus , by tubers , by gemmae and by persistant growing apics . Photoperiod generally favours the development of sex organs in anthoceros . Antheridia and archegonia develop endogenously in closed chambers . Antherozoids are elongated , coiled and biflagellate .
Elongated cylindrical sporangium is characteristic of anthoceros . The sporophyte of anthoceros is made up of capsule and foot ( seta is absent ) . The capsule of anthoceros appears as a long bristle or horn on the dorsal surface of thallus hence the name hornworts has been given to these plants . There is an intercalary meristematic zone between foot and capsule , which is responsible for indeterminate growth of capsule for long period . Sporophyte shows line of dehiscence . Sporogenous tissue develops from amphithecium . Elaters of anthoceros do not have spiral thickenings , therefore they are called pseudolaters . Pseudolaters are 2-3 celled and branched . Calyptra ( involucre ) is extension of thallus .