Volume 4, Chapter 11:- Haworthias – Small Relatives of Aloe

Printed in Excelsa 4:17 (1974)

M. Bruce Bayer

Introduction

            There are few succulent collections which do not include haworthias, although these small and insignificantly flowered plants are not good garden subjects.  Their size, and shade and shelter requirements make them better suited to intensive cultivation in raised containers under shelter.  Very popular with collectors especially prior to World War II, the decline in popularity can be attributed to various factors.  Although the genus is credited with some 160 species and more than 250 varieties, it is highly unlikely that more than 90 species and perhaps 10 sub-species would survive a critical revision.  Many species have been eliminated in recent years, but there are still many maintained only by the mystery of their origin.  Hybrids and ill-defined or inadequate species account for many superfluous names.  The result is an artificial pseudo-scientific system of nomenclature in which the classic binomial system is prostituted for a series of horticultural cultivars.

Within Haworthia there are real problems of definition and circumscription of the species.  The variability within species is often so great that it is very difficult to circumscribe a species in such a way as to exclude members of other species.  The species are best recognised as geographical entities and no species can be described without good reference to locality and distribution.  This is the only way in which a sound system of nomenclature directly related to field complexes, and hence a “natural system”, can be derived.  Names are the fundamental basis of communication concerning the plants, and the psychology of collecting requires good definition of the “kinds” of things being collected.  Nevertheless it is surprising how many persons enthusiastically and vehemently argue the “differentness” of things without seriously considering where the boundaries of difference really lie.  The system of nomenclature in Haworthia has been so confused that it has not been possible for collectors to name or acquire plants consistently or confidently.

What are Haworthias?

The genus Haworthia is currently experiencing another stormy taxonomic passage and for the present includes the genus Chortolirion Berger.  C.A.Parr in the African Succulent Plant Society Bulletin (6: 145, 1971) also included the genera Astroloba Uitew. and Poellnitzia Uitew.  However, the writer refuted this in the National Cactus and Succulent Journal 27: 77 (1972).  This refutation was not considered by Mrs.A.A.Obermeyer-Mauve in her article in Bothalia (11: 119, 1973) where she tacitly supports Parr’s arrangement.

The genus Astroloba comprises seven species, all of which have leaves arranged in five conspicuous rows.  The genus was revised by Mrs. P. Roberts-Reinecke in an unpublished thesis submitted for the degree of Master of Science to the Department of Botany at the University of Cape Town.  This comprehensive work makes a mockery of the recognised species and demonstrates the remarkable confusion that can arise in taxonomic nomenclature.  It is Mrs. Roberts-Reinecke who concludes that there are only seven species with three subspecies, and she also describes the intergeneric hybrid Astroworthia bicarinata (Haw.) Roberts-Reinecke – the hybrid Astroloba rugosa Roberts-Reinecke(nom. nud.) X Haworthia margaritifera (L.) Duval (the latter now H.pumila).  Apart from floral characters, there are no caulescent haworthias with five well-defined leaf parastichies and only Poellinitzia rubriflora (Bolus) Uitew. is strictly comparable.   This monotypic genus has a unique gasteria-like flower and to lump it either with Haworthia or Astroloba is clearly incorrect.  The more recent inclusion of Chortolirion, also monotypic, under Haworthia by Mrs. Mauve is also very questionable.  Certainly her argument in which she presents H. graminifolia G. G. Smith as being bulbous and thus comparable with Chortolirion is erroneous.  H. graminifolia has no semblance of a bulb or fleshy leaf base, although the broad leaf bases do completely enclose the stem.  The real error lies in the unstated contention by both Parr and Mauve, that Haworthia is an integral undifferentiated unit.  This is fallacious, as Haworthia is clearly divisible into at least three very well demarcated subgenera (Bayer, 1970).

The first of these is the subgenus Robustipedunculares Uitewaal ex Bayer.  When Uitewaal proposed this name he was suggesting it as a subdivision of two sections of the genus.  Proper analysis referring to valid natural species shows that there are five species sharing common characteristics.

These are:-

H. minima Haw.

                        H. marginata (Lam.) Steam.

H. margaritif era (L.) Haw. (H. pumila (L)Scott)

H. kingiana Poelln.

H. poellnitziana Uitew. (now H. minima var poellnitziana)

They are all acaulescent with robust branching inflorescences;  unmistakably similar perianth tubes and arrangements of penanth lobes:  rounded seed capsules and black winged seeds.  They all occur in the southwestern Cape with H. margaritifera extending into the Little Karoo and H. kingiana occuring in the Mossel Bay area.  These are essentially winter growing species which flower in mid-summer.  There is some degree of presumed introgression in the case of H. margaritifera and H. marginata in the Ashton area and apparent hybridisation of H. marginata with H. minima around Heidelberg (Cape).

The second subgenus Hexangulares Uitew. ex Bayer was also defined.  It comprises both caulescent and acaulescent species, and the flowers are exasperatingly identical throughout.  The perianth lobes are practically always similarly presented, but small differences can be detected (also in the case of the perianth tube) in some instances.  The peduncle is usually unbranched and the perianth tube is comparatively straight with the veins of the three inner petals positively separating the margins of the outer tepals.  There are not more than twenty species in this group and the distribution is quite extensve.  H. limifolia Marloth and H. koelmaniorum Oberm. & Hardy occur in the B. Transvaal, Swaziland and N. Natal.  The former species is variable so that distinctive geographic types can be recognised.  Thus H. koelmaniorum may still best be recognised as a local element within, certainly having no affinity with H.. tuberculata as suggested by the authors of the species.  H. tuberculata Poelln. is also not allied with the so-called Margaritiferae.  It occurs in the Little Karoo, has the same slender branched inflorescence and narrow slender perianth tube with straight upper tepals as H. starkiana Poelln.  The latter species is fairly localised in the low mountains just north of Oudtshoorn and the hybrid with H. tuberculata probably accounts for “H. smitii” Poelln!

H. tessellata Haw. is very widespread, occurring from south of South West Africa, through the southern Orange Free State to Jamestown (at 6 000 ft.!) and down to the Little Karoo.  H. venosa (Lam.) Haw. is probably a synonym of H. recurva Haw.,  which occurs in the Breede River valley near Swellendam.  It is supposedly distinguished mainly by its longer bigger leaves, but some very small forms occur at Napkysmond to the south, while large forms of H. tessellata occur around Oviston and Graaf Reinet.  In the Ceres Karoo one finds caulescent subscabrous populations which are very close to the distinctive H. granulata Marl.

H. viscosa (L.) Haw. is a strongly trifarious species occurring widely in the Great and Little Karoo as well as the southern Cape. It varies quite considerably at different localities, and species such as H. beanie G. G. Smith, H. cordifolia Haw. and H. asperiuscula Haw. are probably all superfluous.  H. nigra (Haw.) Baker (or H. aspera Haw. if Mrs. Reinecke is correct) is widely spread in the Eastern Cape and Great Karoo.  It is a smallish caulescent dark tubercled species which has been recorded in different forms from as far to the northwest as Loeriesfontein and down to Grahamstown in the southeast.  H. sordida (Roem. & Schult.) Haw. is a comparatively rare species found from Uitenhage westward to Steytlerville — a very slow growing dark species with the same slender 2-3 branched inflorescence as H. starkiana and H. tuberculata.  H. glauca Baker is best known in the glabrous form from the top of the Zuurberg north of Addo, but is undoubtedly synonomous with the slightly tubercled straight leaved “species”, “H. herrei Poelin”., “H. jacobseniana PoelIn.”, “H. jonesiae Poelin.”, and “H. eilvae Poelln”., from the area Uitenhage to Willowmore.

H. reinwardtii (Saim-Dyck) Haw. and H. coarctata Haw. are the subject of a recent paper in the National Cactus and Succulent Journal, and many species and varieties can be excised with rational observation of these two species in the field.  H. reinwardtii occurs from East London to the Fish River and just beyond, while H. coarctata is found westward to Paterson near Port Elizabeth.  These two species are caulescent and are otherwise very close to the acaulescent H. attentuata Haw. and H. fasciata (Willd.) Haw.  H. attenuata is best recognised in the area east of Grahamstown and H. fasciata in the fynbos areas around Port Elizabeth and Humansdorp.  However, H. attenuata also occurs with the very distinctive finely tuberculate H. radula (Jacq.) Haw. in the lower valley areas of Hankey/Patensie.  H. armstrongii Poelln. and H. browniana Poell. both consist of small local populations lying very close to each other north of Uitenhage.  It is possible that they may have arisen by odd hybridisation of H. glauca and H. fasciata and subsequent vegetative propagation.  This is of course highly speculative because no evidence has yet been presented to indicate that hybridisation has led to speciation in Haworthia.

There is no doubt about H. longiana Poelln.).  It has long hard leaves and the offshoots at the stem emerge as strong branchlike out- growths, rather than as softer obviously axillary offsets as in near relatives.  H. woolleyi Poelln, is most easily allied to H. tessellata although it has the proliferous clumping habit of H. attenuata.

The third subgenus Haworthia is perhaps the most complex of all.  These are all acaulescent species (despite “H. ramosa G. G. Smith”) where the peduncle is simple and the outer tepals of the floret have touching margins. The tube is curved and the style upcurved – there is no adhesion between the inner and outer tepals.  There are several very decided species with characteristics which evidence a distant relation.  H. wittebergensis W. F. Barker with its papery leaves, growing in the mountains south of Laingsburg, cannot really be allied with H. angustifolia of the section Loratae.  H. graminifolia G. G. Smith from Schoemanspoort near Oudtshoorn and H. blackburniae W. F. Barker from Van Wyksdorp to west of Ladismith both have fusiform roots and long linear narrow leaves.  H. maughanii Poelln. and H. truncata Schonl. have truncated leaves (to use the vernacular, these are the “perdetande”) and truncation occurs in the second leaf of the seedling.  This is quite unlike the recurvature of the leaves of the section Retusae, although the functional end purpose appears to be the same.  The involved taxonomic confusion presently negates a really rational discussion of the remaining species.  The “Retusae” is a section comprising a vast series of intergrading populations extending from Steytlerville to Bredasdorp in the southwestern Cape.  This series includes many recognisably distinct taxa such as H. springbokvlakensis C. L. Scott, H. comptoniana G. G. Smith, H. parksiana Poelln., H. mutica Haw. and H. mirabilis Haw. etc. where the leaves are strongly reflexed to give an apparently truncated end area.  However, several segregates in the same series have normal suberect or incurved leaves e.g. H. reticulata Haw., H. pubescens Bayer. In H. schuldtiana Poelin. some of the segregates have “retused” leaves and others lanceolate incurved leaves.  The section as it stands at present is an artificial one as some of the principal elements of the series are incorporated in sections such as the Denticulatae Berger and Muticae Berger.

Without good anatomical characters it is virtually a question of guesswork to try and prepare a reasonable diagnosis of the other sections and this may be true of the whole tribe Aloineae.  Chortolirion can be described as having a haworthia-like flower if one very crudely regards the flowers of the haworthias as all alike.  Actually Chortolinon has the straight tube, tepal arrangement and straight style of the Hexangulares.  Whereas there is some difficulty in separating species of that group on floral characters, Chortolirion stands out like a sore thumb.  The florets are practically sessile with wide pedicellate attachment while the

peduncle is relatively short, fleshy in comparison with Hexangulares and notably glaucescent.  Vegetatively Chortolirion has a distinct bulb, the leaves tend to spiral, they have the white markings characteristic of the Leptaloe and the plants are deciduous as is Aloe kniphofioides – the die-back of the leaves is not directly due to fire or frost as suggested by Mrs. Mauve, but a seasonal phenomenon.  H. graminifolia in the subgenus Haworthia does not have the semblance of a bulb and it would take more than “eliminating gravity” to get the floret to resemble that of Chortolirion.  Mrs. Mauve is also responsible for the inclusion of Chamaealoe africana in Aloe as A. bowiea Roem. & Schult. f.  While in essence her treatment may be correct, the facts mobilised in support do not substantiate the change.  No one can claim that the generic states in the Aloineae are or were factually correct, but there seems to be little point in merely guessing at a better construction.  What is needed is a thorough anatomical study of the entire tribe to include all the genera and aberrant species.  Any other basis for creating and recreating categories is unsatisfactory.

The cultivation of haworthias:

The success of any plant in general cultivation is more certainly a product of inherent adaptability and vegetative or seed fecundity, than dependant on any skills of the gardener.  The principal basis of speciation in plants is undoubtedly geographic distribution and habitat selection, so that there are many kinds adapted to specific microhabitats.  Any collector attempting to grow all the species of any respectably sized genus must face either fact or disappointment.  To be successful the collector must provide “intensive care” facilities for the inevitable difficult plants . Haworthias are no exception to the rule.  The gaps in comprehensive collections are not only due to a taxonomic situation loaded with “species” that are not, but also due to species which require luck or skill to cultivate successfully.  Of all the variables which affect success in cultivation, soil is perhaps the most complex.  Variability in soil seems to play a major role in determining the composition and distribution of plant communities.  Haworthias are largely associated with rocky situations with undeveloped soils and it is surprising that most can be grown in the standard soil mix consisting of one part loam: one part sand: one part compost.  J. R. Brown, the American doyen, concluded that Haworthias could be grown in almost every type of fairly porous well drained soil.  This is mostly true but attention must be paid to shade and watering.  Practically all the species occur naturally in shaded conditions and require semi-shade in cultivation.  Mature plants are often found in exposed positions in the wild, but these are invariably highly coloured, stunted, withdrawn into the soil, or the leaf tips are necrotic.  The best colours and forms are of course obtained with the least possible shade and attenuation or yellow chlorosis of the leaves should not be tolerated.

Watering is a very critical factor and it must be remembered that there are species from the southwestern Cape adapted to winter rain.  Conversely there are species averse to winter wetness.  There is no fixed principle that winter growers flower to set seed for the start of a new growing season, so flowering is not a good indication of water requirement.  H. herbacea and H. reticulata flower in early spring, H. margaritifera in mid-summer, and H. schuldtiana in early winter, yet they are all winter growers.  The winter rainfall area is really demarcated by a line drawn from Bredasdorp to the mouth of the Orange River.  Rainfall immediately east of this line comes mainly with the autumn and spring solstices, but growth is mainly in winter as a result of adaptation to the intense summer heat and low humidity.  East of Ladismith the species appear to be mostly summer growing.  In practice the winter growers require a dry spell in late summer.  There are some species which have an indeterminate growth cycle, e.g. H. setata Haw. and H. venteri Poelln., and injudicious watering can quickly lead to disaster.  If in doubt it is best to water when the plants show indications of stress, always bearing in mind that shade may be more desired than water.  With some of the really slow growers such as H. sordida and H. woolleyi the temptation to water may be an invitation to the compost heap.  They cannot be pushed into vigorous growth and increased shade is again more likely to produce the required results than water.

The summer rainfall soft-leaved Haworthias tend to lose all their roots with winter watering but it is not wise to generalise.  H. pilifera cannot be put in the same class as the cliff-hanging (literally) H. cymbiformis/ planifolia types.  These types are very proliferous and want particularly good drainage below, and a dry winter.  H. pilifera will tolerate poor drainage if its water comes sparingly and at the right time.  The best specimens are grown in quite intense light conditions forcing retraction into the soil as is their wont in nature.  In some variants the leaves may completely truncate with a network of necrotic veins to screen out the sun.  In this respect many haworthias resemble the windowed “mesems” such as Fenestraria, Lithops etc. which reduce surface area (and transpiration) and make provision through surface translucency, for photosynthesis by sunlight in the deeper buried chlorophyll-bearing tissue.  Retraction into the soil is a characteristic of the thick-rooted species such as H. truncata and the “retusae”.  It is thought to be brought about by contraction of the roots pulling the plant down into the soil.  If plants are excavated and allowed to dry out, the roots flex very strongly upwards which would also have the effect of forcing the stem down.  However retraction occurs, it is puzzling how the soil is displaced underneath the plant, because H. truncata, among others, may be found in the stoniest of ground.  Retraction should thus not be regarded only as a movement per se of the plant downwards, but a state into which the plant grows from the time of germination.  If retracted plants are transplanted and well submerged in the soil, the chances of losing them from overwatering are increased.  Overwatering can be defined as a combination of giving too much water too often, poor drainage, poor ventilation and incorrect nutrition.

The Hexangulares species such as H. attenuata, H. reinwardtii and H. coarctata are the commonest encountered in gardens.  This is because they are very prolific vegetatively, fairly fast growers, and very much more tolerant of exposure to sun.  Members of this group seldom have surface translucency and are generally not retracted.  H. tessellata grows in very very hot situations but usually in the protection of rock crevices and under stones.  H. limifolia is also found where it can get very hot, but survives under the protection of bush or grass canopy. A common species in gardens is a highly fasciated form of H. attenuata which is usually taken to be H. fasciata.  The latter species has less attenuate leaves and the upper leaf surfaces are smooth.  H. fasciata is not a common species in gardens and this can only be accounted for by soil requirement.  The species is found in the acid soils of the Port Elizabeth/Uitenhage area where it grows in the “fynbos” vegetation and exemplifies the problem of suitable soil for cultivation.

Several species are found in the Robertson Karoo in undeveloped soils of the Malmesbury shales.  The vegetation is highly differentiated into distinct plant communities over very small distances.  Soil pH may vary from 3,9 to 7,8 over a distance of ten paces.  However soil pH is not an only consideration.  H. margaritifera is found usually in Pteronia paniculata (the composite “ribbokbos”) communities where pH varies between 3,9 and 4,9.  It also occurs in Ruschia carolii (Aizoaceae — vygie or mesem) communities where low pH (4,8) is also recorded and where H. herbacea may be plentiful.  It is not unusual for the situation to be reversed with H. herbacea in the Pteronia communities and H. margaritifera in the Ruschia.  Yet it is clear that each species has very specific requirements and does not ever appear to co-habit in a single locality.  It is often the case that three or four species of Haworthia grow in the same general locality, but clearly confined to their own microhabitats within a stone’s throw of one another.  Neither H. margaritifera nor H. herbacea is successful in general cultivation and the reason appears to be a combination of their winter rainfall requirement and their soil needs.  H. marginata is similarly rarely successful in cultivation and also (or co-relatedly) rare in habitat.

Propagation of haworthias is more often than not by vegetative offset, as most of the easily cultivated species are also very prolific.  Pure seed is not generally available because of the tendency to hybridise, and the plants take three to four years to reach maturity from seed.  Seed is easy to obtain by cross-pollination but the parent plants must be isolated from the insects and birds that normally pollinate them.  The plants are self-sterile and so the parent plants must be from genetically distinct clones.  Pollination is simply effected by inserting a fine hair into the floret of one plant and transferring the adhering pollen to the other.  Pollen is released from the youngest flowers and the older flowers bear the receptive stigmas.  Pollination is dependent on ideal weather conditions and warm sub- humid mornings are ideal.  The seed capsules begin to form immediately after successful pollination and the fertile capsule may ripen in weeks.  Failure of pollination. marked by the early abscission of the pedicels.  Seed is best sown fresh, in early winter for the winter growers and any time in the summer for the summer growers.

A well-drained loose soil is used, with the seed very lightly covered with the same soil and lightly topped with a thin layer of small pebbles to hold the germinating seeds and tiny seedlings.  Where damping- off is a problem, soil sterilisation may be practised or fungicides used.  Transplanting follows crowding and must take place with due respect for the growing season and condition of the seedlings.  Experience indicates that young plants should first be subject to some drying out and the young seedlings transplanted with intact roots, and then lightly watered.  Older mature plants should also be well-rested before moving and if not, all the roots should be stripped off before replanting.  Water should also be withheld for a few days after planting and the plants shaded until they start to grow again.  Haworthias root best from the stem area closest to the lowest leaves and it is unwise to leave a big section of stem, or plant deeply with the expectation that roots will develop all along the submerged portion.  Many species will propagate from leaves but this is a haphazard venture unless properly done.  The leaves must be removed as closely as possible to the stem to ensure removal of adventitious growth tissue with the leaf.  Gasterias can propagate from portions of leaf, but not Haworthia.  Like aloes, non-dividing species can be induced to multiply by damage to the growing point the difficulty in this technique lies in inducing oneself to inflict the necessary damage on a treasured rarity.  Excised leaves may be stuck shallowly into a sandy soil-mix and weighted down with small stones if need be.  Propagation may also be effected by cutting entire plants into section and treating the cut surface with sulphur or some other fungicide.  The writer cannot claim to having achieved any success with rooting hormone but it does seem to produce a good healing of broken surfaces.

 

Conclusion:

The published literature on Haworthia prompts one to misquote… “never has so much been written, about which so many know so little!”.  Inadequate descriptions, erroneous naming and confused names seem to be the lot of succulent plant groups where the degree of amateur interest has greatly exceeded that of the botanist.  E. J. Bullock made some apt remarks concerning the amateur in “Thoughts on the status of Aloe lutescens” in Excelsa No. 3.  It is fortunate that there is no such thing as “closed shop” in taxonomic botany but it still behoves the prospective taxonomist to be aware of the levels at which information might now be available.  The making of an herbarium specimen and concoction of a latin description are very elementary barriers to the determined author of a new name.  However, the development and maturation of a suitable species philosophy is another matter altogether.  Since Darwin and perhaps before, there has been no complete accord on a definition of the “species” although almost everyone has a good idea of what it is.  All can agree that the species is the basic unit of classification and it is also fairly easy to accept the classic definition of a species as a grout (or groups) of interbreeding or potentially interbreeding individuals.  It is only in the last 30 years that the qualification has been added where all barriers to sexual reproduction are included.  However, the difficulty really lies in the fact of change, so that any definition needs to consider variability in a species as it is exhibited in both space and time.  There may be groups of plants which are currently not broken into clearly discontinuous groups which can be readily recognised as species.  Often the case is that where some elements of a group form very clear subgroups and so species, other elements are highly variable.  The former group suggests completeness of adaptation which has been said to be “cause of senescence of the issue”.  In other words a well adapted and nonvariable species has probably lost the genetic capacity to change with changing environment and is so threatened.  Alternatively, the highly variable “species” or aggregate of elements has the genetic resources to meet changes in the environment.  In Haworthia the variable elements are often highly localised and it does not seem possible to evaluate these properly as species or otherwise.

G. W. Reynolds can be considered to have done remarkably good work with Aloe classification for the period in which he worked, and perhaps for much later too.  However, no one can contest that problems do not still exist in that genus, and not only at the level of the species.  The genus concept in the Aloineae is under pressure as witnessed by the changes implemented by Parr and Mauve.  That this pressure has been characterised by a lack of valid new information on which a better grouping can be based, merely serves to emphasise the fact that sound arguments for the older situation never existed.

(This article was accompanied by colour illustrations).