PERSOONIA

Published by the Rijksherbarium, Leiden

Part Volume 6, 4, pp. 389-394 (1972)

Ascocarp ontogeny and a natural classification

of the Ascobolaceae

J. van Brummelen

Rijksherbarium, Leiden

(With 1 diagram)

has be useful basis for the classification Ascocarp ontogeny proved to a very of the Ascobolaceae. A scheme of interrelationships between the sections

of It is that and is given. suggested ascocarp ontogeny

will taxa play a prominentpart in recognizing series of supra-specific within

other natural families the of Discomycetes, e.g. Thelebolaceae and Pyro-

nemataceae.

the the Ascobolaceae and their allies include Among many objects

suitable for developmental studies. The coprophilous species in particular can often be isolated and artificial media. easily grown on

Since Yu's factors the favourableconditions experiments (1954) on concerning most for in some of Ascobolus several ascospore-germination coprophilous species , species have been studied that could not be cultured before. The development of Discomy- cetes that do not produce fruit-bodiesin culture is usually incompletely known. Publi-

have been cations on the sexuality, compatibility and cytology of such species that cultured contain deal of informationfrom which data a great many on ascocarp

be deduced. The of the of the ontogeny can development sporophytic part ascocarp in particular has drawn the attention of investigators in these fields of research.

Unfortunately identifications can only rarely be verified. Studies devoted to the ontogeny of both gametophytic and sporophytic parts of the ascocarp of Dis- comycetes are very rare.

Corner's classical laid basis for publications ( ig2ga, ig2gb, iggoa, iggob, iggi) a a comparative morphology of Discomycetes with special emphasis on the dynamic

of did result in increased interest in aspects ascocarp ontogeny. This, however, not an the and of of until the last problems significance ascocarp ontogeny Discomycetes decennium. Recently the Ascobolaceae and their allies have been the subject of ontogenetic studies by Gamundi & Ranalli (ig6g, ig64, ig66, ig6g), van Brummelen

(7967), and Durand (igyi).

METHODS

In developmental studies of Discomycetes the results of three methods should be combinedto obtaina complete structural and functional image ofascocarp ontogeny.

* Paper read at the Symposium " of operculate Discomycetes" held at the First International Mycological Congress, Exeter, 1971.

389 Persoonia Vol. Part 390 6, 4, 1972

sect. Ascodesmis iodine none Ascobolus Pseudascodesmis

with

ascus-wall weak sect. obolus or the Ascobolus Gysnnasc of medium sect. Ascobolus I J/ ■/

: DIAGRAM staining Ascobolus Sphaeridiobolus > i sect. \ blue Ascobolus sect. Pseudo- saccobolu3 sect.

\ Ascobolus Heimerlia strong Ascobolus Dasyobolus \

Saccobolus sect. triobolus Saccobolus sect, oaccobolus

ascoma ascoma, asooma, telohy- ascoma, late ascoma, mid-meso- ascoma, early asooma, prohymen- ascoma asooma the -phase the phase ascoma the the phase the excipulum excipulum in in opening in phase in in of phase an cleistohymenial oleistohyraenial oleistohyraenial mesohvnenial cleistohymenial hymenial cleistohymenial raesohymenial cleistohymenial paragymnohymenial eugymnohymenial eugymnohymenial type never opening menial opening opening opening opening ial with without J. van Brummelen: Classification of Ascobolaceae 391

Besides a study of vital and stained microscopic preparations of whole mounts of

microtome the earliest stages (initiation) extensive investigations of series of

sections different showing stages are indispensable (topographic onto-

geny). Omission of this methodhas led to erroneous interpretations and unaccept-

be differentiated able generalizations. In several cases hyphae ofvarious origin can

third is to by staining. A method (Corner's hyphal analyses) an attempt

trace hyphae from their origin to their end or vice versa through their elaborate

of organization in the fruit-body. In hand-made sections or oriented fragments

the the tissue, elements are separated by gently pressing cover-glass or pulling hyphae

with needles. this method also does much in Unfortunately, not help very unravelling

the often perplexingly intricate structures of the early stages of the ascocarp.

ASCOCARP ONTOGENY IN ASCOBOLACEAE

The first indication initiation is the in the of ascocarp development mycelial

hyphae of weakly to strongly curved and swollen branches. Of these archicarps

one or more terminal or subterminal cells differentiate into multinuclearascogonia.

Antheridia are also often found. In certain species parthenogenetic or apogamous

have been processes reported.

From the base of the archicarp or from adjacent mycelial hyphae, and shortly before the These branch and or after differentiationofascogonia, thin hyphae arise. form an incomplete or continuous sheath around the archicarp. This primary sheath is the of the of the In of develop- beginning gametophytic part ascocarp. open types ment, i.e. with gymnohymenial ascomata, the investing hyphae of the primary sheath have only a restricted growth in that they do not form an entire sheath over

i.e. the hymenium during further development. In closed types of development, with cleistohymenial ascomata, the investing hyphae produce a continuous primary sheath. Thus small spherical bodies are formed. Usually there is a more or less

of centrally placed archicarp with a strongly swollen ascogonal apparatus in each them, surrounded by intricate investing hyphae. Often the cells of the primary sheath undergo a change in becoming inflatedand thick-walled, while their growing activity slows down.

Observations in species of Ascobolus with cleistohymenial ascomata have revealed that certain of when the sheath has reached a at a stage development, primary thickness ofonly a few layers ofcells, a secondary sheath develops within it. The same has been observed in species of Thelebolus, while Durand (igyi) described a similar

development in a species of Lasiobolus. The hyphae of this sheath are relatively narrow and have dense cytoplasm. They arise near the base of the archicarp. Unfor- tunately it was not possible to establish with certainty from what cells they originate.

As a result of the active growth of hyphae of the secondary sheath within the

sheath primary tangential forces are exerted on the peripheral layers. Depending on the structure and growth activity of the hyphae of the primary sheath different cortex-textures will result. cells become break into Peripheral may flattened, or up Persoonia Vol. Part 392 6, 4, 1972

small later the results in smooth and groups. During development process rough

surfaces respectively. Both kinds are found in cleistohymenial ascomata of Ascobolus,

Thelebolus, and Lasiobolus.

Peripheral gaps are also filledby interstitial growth ofnew elements fromthe inner

layers. During further development hyphae of the secondary sheath form the medulla

in the lower and the of the of the part palisade paraphyses in upper part young

ascocarp.

There is a striking resemblance between the development of cleistohymenial

ascomata in Ascobolus and its allies and the developmental scheme given by Doguet

f° in ( 1.955) r perithecia Melanospora.

From the Their first cells multi- ascogonia ascogenous hyphae grow upward. are the nuclear. Soon branches are sent out whose cells are dikaryotic. On reaching

thin layer of small plasm-rich cells at the base of the paraphyses these branches

spread centrifugally, with frequent sympodial ramification. Their cell-divisions are

accompanied by conjugate nuclear divisions. The croziers, terminally formed on this

sympodial system, grow up from between the bases of the paraphyses and give rise

to the asci. The incipience, development, and ripening of the asci proceeds in a

centrifugal direction; the oldest being in the centre of the hymenium.

Further of the is about intercalation development ascocarp mainly brought by Ascobolus of new elements and subsequent strong inflationof asci. Only in species of

is there sect. Gymnascobolus a submarginal secondary growing zone (cf. Corner,

1929a).

The types of development in Pezizales are distinguished by the developmental

in which the phase hymenium becomes exposed. In an earlier study (van Brum-

of introduced. melen, 7967) two sets descriptive terms were

During ascocarp ontogeny five phases were distinguished in respect to the ripening ofthe hymenium. These chronological phases were named (1) archihymenial

before the initials of the phase: hymenium are present; (2) prohymenial

but croziers phase: paraphyses are present no are as yet formed; (3) mesohy-

menial phase: the hymenium is in progress of ripening, but no asci have as yet ripened; (4) telohymenial phase: mature asci are present and normally

and the ascospores are discharged; (5) posthymenial phase: hymenium becomes overripe or obsolate and decomposes.

With regard to the hymenial development two main types of ascomata were

distinguished. (I) Cleistohymenial ascomata in which the hymenium is

least its Ascomata of this be enclosed, at during early development. type may

further subdivided according to the hymenial phase when they open to expose the

hymenium. (II) Gymnohymenial ascomata: the hymenium is exposed

from the first until the maturation of the asci.

Two of the latter subgroups were recognized :(a) paragymnohymenial

ascomata in which the ascogonium is overarched by investing hyphae of limited

that do form sheath growth not a continuous and (b) eugymnohymenial

ascomata with a fully exposed ascogonium. Brummelen Ascobolaceae J. van : Classification of 393

By the use of these unambiguous terms a more detailed differentiationin develop-

mental is than before. Of the Brum- types possible seven types recognized (van

melen less than six within the Ascobolus and Saccobolus. 1967: pi. iy) no occur genera

CLASSIFICATION

In my opinion the genera Ascobolus and Saccobolus form a very homogeneous and

natural of which be the rank of group operculate Discomycetes, can given family

the existence of violet of vacuolar (cf. Rifai, 1968). Especially a episporial pigment

origin is a unique character which unites these fungi. Between the Ascobolaceae and

other Pezizales with relations and coprophilous protruding asci the are more remote

less clear.

For a subdivision ofthe Ascobolaceae in taxa oflower rank the following structural

characters be of the of asci and proved to importance: shape ascocarps, ascospores,

the cortical texture, the ascospore-arrangement, and the reaction of the ascus-wall

with iodine.

If the taxa of the Ascobolaceae are classified according to these structural criteria

the of each show the of only, resulting groups species same type ascocarp ontogeny. concatenated in Exactly the same groups will be arrived at if the species are series of over-all similarities (classification 'par enchainement').

By classifying the Ascobolaceae according to the ontogeny of the ascocarp,

useful classifi- supplemented with some of the structural criteria mentioned, a very cation is obtained which reflects empirical relations.

The Ascobolus is distinguished by the mutually free ascospores, which are

not arranged in a regular package during any phase of maturation. In Saccobolus

the united into cluster less ascospores are firmly or loosely a according to a more or

of regular pattern arrangement. section In Ascobolus seven sections were recognized (van Brummelen, 1967: 63):

with that before the Dasyobolus cleistohymenial ascomata do not open telohymenial

phase; section Sphaeridiobolus with cleistohymenial ascomata opening in the late

mesohymenial phase and globular ascospores with rounded warts; section Ascobolus

with cleistohymenial ascomata opening in the early or mid-mesohymenial phase;

section Pseudascodesmis with paragymnohymenial ascomata, the habit of Ascodesmis, and the ascus-wall blue with section Pseudosaccobolus with not staining iodine; para-

the habit of Saccobolus and the ascus-wall or eu-gymnohymenial ascomata, staining

deep blue with iodine; section Heimerlia with small eugymnohymenial ascomata and

the cortex scarcely developed; and section Gymnascobolus with eugymnohymenial

ascomata with an active submarginal growing zone.

Saccobolus was divided into two sections, section Saccobolus and section Eriobolus, both with paragymnohymenial or more rarely eugymnohymenial ascomata. These

in two sections, although slightly differing ascocarp ontogeny, are distinguished on

the basis of structural characters, such as pigmentation and ascospore-arrangement.

A tentative scheme of interrelationships between the sections of Ascobolus and Persoonia Vol. Part 394 6, 4, 1972

the Saccobolus is given in diagram on page 390. In this scheme the sections are arran-

from the downwards their from closed ged top according to ascocarp ontogeny fully

to fully open. In the same sequence there is a decreasing growth-activity of the

hyphae of the primary sheath; especially in the archihymenial phase.

CONCLUSION

has be useful basis for the classification of Ascocarp ontogeny proved to a very

the Ascobolaceae. It may also help in recognizing series of supra-specific taxa

within other natural families of Discomycetes. The Thelebolaceae and the Pyro-

in this nemataceae particular are promising objects in respect.

It would be of the of include in great importance to taxonomy Discomycetes to

principle the stages of ontogenetic development in the comparative study of cha-

racters.

In the past extreme types of ontogenetic development ( , Thele-

bolus stercoreus, and Ascodesmis) have been the starting-point of far-reaching specu-

lations on relationships within the Ascoraycetes.

We must always be on guard, especially in ontogenetic and morphological

studies, not to base generalizations on the study of a single or only a few taxa.

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