In this article we will discuss about the features and classification of heterobasidiomycetidae.
Diagnostic Features of Heterobasidiomycetidae:
(i) Lack dolipore septa and clamp connections. Recently, however, clamp connections have been recorded in many species.
(ii) Formation of thick-walled binucleate spores known as the teleutospores.
(iii) Basidium partitioned transversely or longitudinally into two, three or four cells (phragmobasidium).
(iv) The basidia result from the germination of a thick-walled, resting spore (teleutospore).
(v) The ripe basidium divisible into two parts, the basal part called the hypobasidium and the distal part termed the epibasidium.
(vi) Basidiospores borne on the epibasidium may be sessile or stalked.
(vii) Number of basidiospores per basidium may be four or more than four.
Classification of Heterobasidiomycetidae:
There is a great controversy with regard to the classification of this sub-class into orders and families.
Martin (1971) divided the sub-class into the following three orders:
(1) Tremellales:
Most of the members are saprophytic but some are parasitic on higher plants, mosses or insects. The saprotrophs are common on dead tree branches and decaying logs.
The mycelium produces a well-developed fructification called the basidiocarp. It has a jelly-like, waxy or cartilaginous texture. The basidia are arranged in a hymenial layer over the surface of the basidiocarp. Popularly the Tremellales are called the jelly-fungi.
(2) Ustilaginales:
It includes the smut fungi which mostly parasitize higher plants. Basidiocarp is absent. Basidia are developed by the germination of thick-walled resting cells (teleutospores) which are usually black and called the smut or brand spores.
The basidiospores are sessile and irregular in number. They are not discharged forcibly.
(3) Uredinales:
They are obligate parasites of certain seed plants and ferns and are called the rusts. The basidiocarp is absent. The thick-walled resting cells are two-celled structures called teleutospores.
They are brown to black in colour and on germination give rise to basidia. The basidiospores, which are stalked, are discharged forcibly. Each basidium usually produces four basidiospores.
In the Ainsworth’s (1973) system of classification, the class Teliomycetes has been divided into two orders Ustilaginales and Uredinales.
While in the order Ustilaginales, the basidiospores are sessile and passively released, in the order Uredinales, basidiospores are produced on short pointed sterigmata and are forcibly discharged.
The orders Ustilaginales and Uredinales are discussed in some detail.