Monday, 6 July 2015

Haworthia marxii explained.



(The revised article below was originally published in Alterworthia International Vol. 12 (2) July 2012: 15-28.)


An honorary Ariocarpus in Africa.
Notes and updated information regarding Haworthia marxii S.D. Gildenhuys.
Gerhard Marx.

It is both exciting and very frustrating to have such a unique Haworthia named after oneself. This species is truly a unique and exciting phenomenon that begs to be properly studied and discussed. For various reasons I remain one of a handful of people who had the opportunity to study it closely in the wild and in cultivation to date. And yet, the frustrating part is that any discussion offered for publication by myself might immediately be interpreted as an egotistical obsession with the plant purely because it was named after me.
A few years ago, after becoming familiar with this strange and unique Haworthia, I informally referred to it as Haworthia ariocarpioides. That was also the name that I recommended to Sean Gildenhuys when he decided to formally publish the species. Today, ten years later, I am even more convinced that H. ariocarpioides would have been a very appropriate name. H. marxii has proven to be by far the slowest and most challenging Haworthia within the subgenus Haworthia to grow and propagate. It also shares the flattened spreading tubercles-like leaves, dull dark colour and slightly scabrid epidermis of Ariocarpus cacti including the feature of having dirt and debris sticking to the newer growth in the wild.
As a result of its slow and difficult propagation, H. marxii is still relatively unknown and very rare in cultivation and enthusiasts can’t be blamed for not knowing what to think of it. Haworthia publications during the past ten years were not any help either, as it is clear that several authors did not quite know what to make of it. Initially the easiest solution seemed to have been to reject it as synonymous with H. bayeri on basis of a few shared features or the geographically closer H. emelyae/ picta. In The 2009 ‘haworthia for the collector’ book of Rudolf Schulz,  H. marxii  was simply listed in the appendix as a synonymn of  H. pygmaea var. splendens “(sic) !? One can only wonder in amusement how on earth such a far-fetched combination was reached!
Fact remains, time always gradually reveals the truth and in some recent species lists it has been recognized as the unique and interesting phenomenon it is.

Meanwhile, let me briefly share my experiences and observations to date:

Habitat and geography:
The history of the discovery of this species was fully discussed in an article in ALOE 44:2:2007 (34-37). In short, it was first found during the late 1980’s but not successfully grown or properly studied and efforts to recollect it were unsuccessful. It seemed to have become largely forgotten during the 1990’s although Bayer briefly referred to it as a form of H. bayeri in Haworthia Revisited (1999). 
The locality was given as the Rooinek pass, south of Laingsburg, which is more than 150 km to the north-west of the known distribution of H. bayeri. This seemed such an unusual occurrence which begged for proper investigation. As a result I did numerous and unsuccessful searches for a number of years before finally locating it during 2005.
The main reason for my many fruitless pursuits was that I was searching for the usual type of habitat that retuse-leaved species like H. bayeri and H. emelyae generally occupy: gentle slopes that are densely covered with quartzite or ferricrete pebbles. In contrast, H. marxii grows on rather steep vertical south-facing rock walls and deeply hidden amongst crevices and small pockets of soil. As a result, the plants are mostly growing rather squashed and uncomfortably flattened in these crevices. Only rarely can one encounter a plant that developed in a large enough space to spread its leaves to full extent. 

A common situation for H. marxii in the wild: tightly compressed in a narrow rock crevice.


The largest and most impressive plant encountered in habitat. The elongated leaves remind a bit of H. badia.
More than 80% of the plants never receive any direct sunlight and most other retuse-leaved haworthias growing in such shady situations would be fresh green and etiolated. However, H. marxii features a distinct dark purplish-black-green colour despite growing in such very shady situations. 

Hiding in a dark sheltered situation on a south-facing slope. This plant is one of many that never receives any direct sunlight in habitat.



Haworthia wittebergensis also grows in the same general area and a small number of H. wittebergensis plants occur even amongst H. marxii. On an adjacent hill H. wittebergensis grows a bit more numerous and together with a form of H. arachnoidea ( =H. isomorpha Breuer). Intensive searches in the surrounding area yielded several more populations of H. wittebergensis as well as the H. arachnoidea, but  H. marxii seems very rare and has not been found outside an small area of about a square kilometre.  
The semi vertical rocks at these habitats are Witteberg quartzitic sandstone and H. marxii shares its habitat with several other succulents like Euphorbia multifolia, a miniature Gasteria (probably disticha), Astroloba smutsiana, Crassula hemisphaerica and Aloe comptonii.  

Photographed on an adjacent slope to a H. marxii population: H. arachnoidea (isomorpha) (left picture) and H. wittebergensis (right).

The co-occurrence of H. marxii, H. wittebergensis and H. arachnoidea presents us with an unsolved mystery: All three of these elements are members of the subgenus Haworthia and all three share more or less the same flowering period!  Which means there seems no clear reproductive isolation measurement at work to prevent these three components from interbreeding in the wild. And yet, not a single natural hybrid has been seen to date. For example, near Dysselsdorp where H. arachnoidea grows close to H. truncata, quite a few natural crosses have been observed.
The other big question that remains concerns the closest relationships of H. marxii. Is it a retusoid element that found an unusual home in rock crevices in the mountains or could it be a H. archeri relative that mimics the retuse-leaved habit?
The possible but unconfirmed report of H. emelyae ca 30 km to the south near Ladismith comes to mind but a close relationship with H. emelyae does not seem obvious due to the various morphological and flower differences which will be discussed below.
A more likely retusoid link seems with the H. maraisii-mirabilis complex. H. marxii shares to some extent the dark colour normally associated with H. maraisii as well as the thin flower peduncles and mid-summer flowering habit. The closest H. maraisii-like element can be found 60 km to the south on Klein Doringrivier farm east of Barrydale.  South-westwards towards Montagu H. maraisii occurs again but this is a good 80 km away. However, in terms of flower similarity, it is the form of H. maraisii growing even further away on the Rooiberg west of Robertson that comes closest to that of H. marxii. See illustration below for comparison.
Haworthia maraisii growing at Klein Doornrivier, ca. 60 km to the south of the Rooinek Pass. Many plants here are identical to H. maraisii as found at Stormsvlei

Another comparison would be to link H. marxii to the H. archeri-nortieri group. There is a collection of Peter Bruyns (PVB 1405) of a H. archeri-like plant only 20 km to the south-east of the Rooinek Pass. I have not been able to locate this population although it is widespread in cultivation and was given the name H. nudata by Dr Hayashi. Typical H. archeri grows much closer and can be found only 10km north of the Rooinek Pass at Viskuil ( JDV 89-62) . These plants also share the same flowering time and some flower features with H. marxii as well as to some extent, the dark leaf colour.

Haworthia archeri growing ca 8km north of the nearest H. marxii to the west of Viskuil. (photo: Martin Scott).

However, all above comparisons with geographically close Haworthia populations remain very speculative and none truly convincing.
Let us take a closer look at other possible associating characters:

Morphology:
H. marxii is characterized by having very dark-coloured and somewhat flattened swollen leaves, spreading outward as generally found in retusoid species. The rosette of H. marxii is therefore much more flattened when viewed from the side than the average retuse-leaved Haworthia. The photos below show such comparisons with H. bayeri and H. emelyae as examples. In H. emelyae and H. bayeri  the leaves recurve abrubtly to form a flattened end area above. In H. marxii the recurved angle is rather gradual and less abrupt. 

Side-view plant profile comparisons between H. emelyae (left) ,H. marxii (centre) and  H. bayeri ( right).


On above photographs another distinct difference is also visible and that is the poor root system of H. marxii in comparison to the others. It is also this fact that causes H. marxii to be of such slow growth and rather difficult to maintain in cultivation.

Seen from above, the facial lines and patterns of H. marxii do remind more of H. bayeri than of H. emelyae .  The facial lines are generally thinner and more numerous in H. marxii and the variation in patterning on leaves of the same plant is very noticeable in H. marxii and much less so in H. bayeri. No two leaves are exactly the same in H. marxii. Features shared with H. emelyae is that H. marxii also has some small floating flecks in-between the facial lines which are lacking in H. bayeri and occasionally the facial lines of H. marxii may also have opaque islands inside the lines as in H. emelyae.

Detail of a rosette to show that some leaves of H. marxii can have dark opaque islands inside the lighter facial lines.


Flower features.
During my initial observations and experiences with H. marxii, and before having seen its flowers, I was convinced for several months that it was a member of the subgenus Hexangulares (now the separate genus Haworthiopsis). This was due to its slow growth, weak roots and vague resemblance to species like H. koelmaniorum, particularly its variety mcmurtryii. Even when the flower peduncles developed for the first time, the very thin flower peduncle was a further reminder of the type found in the Hexangulares. But then the flower buds appeared and opened and I had to stare in amazement that those were not Hexangulares flowers, but typical subgenus Haworthia florets.
The florets actually seemed closer in appearance to those of H. truncata than to H. emelyae or H. bayeri. The upper perianth lobes are not curved upwards like in H. bayeri or H. emelyae but straight. This drew the attention back towards H. archeri and in particular its variety dimorpha that also has such straight upper perianth lobes.  

Side-view plant profile comparisons between H. marxii (left) ,H. emelyae (centre) and  H. bayeri ( right).

In most populations of H. maraisii the flowers also have upward-curving upper lobes and the flowers are generally smaller with narrower lobes than those of H. marxii. Only recently did I notice the rather close resemblance between the flowers of H. marxii and those of the H. maraisii form growing on the Rooiberg west of Robertson ( =JDV 95-1). The upper perianth lobes of the H. maraisii are still a bit upward curving but less so than in other populations of H. maraisii. The flowers of JDV 95-1 are also larger than the average H. maraisii and compares very close in size to those of H. marxii.

Left: Flowers of H. maraisii (JDV 95-1,Rooiberg, Robertson) on the left and H. marxii (GM 623) on the right.  Virtually identical except for the slightly upward curving upper perianth lobes in H. maraisii. Right : a typical plant of H. maraisii JDV 95-1 in cultivation.

As mentioned above, the thin peduncle of H. marxii also compares closer to H. maraisii and allies than to those of H. bayeri and H. emelyae. In fact, even from the stage when the inflorescence bud first appears from amongst the leaves, the differences are already drastically obvious: those of H. bayeri and H. emelyae are three times more thick and robust than the inflorescence buds of H. marxii and H. maraisii.
Then, of course, the time of flowering in the wild is also of significant importance as it is part of nature’s way of keeping elements reproductively isolated.
H. marxii forms part of the summer-flowering group which includes amongst the restusoid species the entire H. mirabilis-magnifica-maraisii group as well as H. truncata and its variety maughanii. The first H. marxii flowers open each year during the first week of February if there had been sufficient rainfall.
H. emelyae and H. bayeri start flowering in August and flowering can continue throughout September into early October. 

Similar peduncles and also developing during the exact same time of the year: H. archeri var dimorpha (left) and H. marxii (right).


It should be mentioned that above discussion of H. marxii was presented in the logical sequence which involves the discovery and familiarizing oneself with any newly discovered element. First one is naturally confronted with the specific geographical situation which should obviously be considered against the presence of other known Haworthia populations in the surrounding area. At the same time one inevitably studies and compares the plants morphological features to other known species. However, often the plants as encountered in the wild do not reveal the full extent of their inherent features and those may only become apparent after observing it in cultivation over time. One can’t for example tell from brief habitat observations what the growth rate of a plant is and how easy or difficult propagation from seeds might be. Then, lastly, detailed observation of flowers and flowering time needs to be documented as this is often the most important barrier used by nature to ensure reproductive isolation.
Therefore, when it finally comes to any taxonomic decisions to be made, the above-discussed sequence of discovery and familiarizing automatically gets turned around and the formal documentation involves working backwards through these facts, from the less obvious and finer specific details of the reproductive organs to the obviously observable general plant features and geography. With other words, flowers and flowering time needs to be considered first, then plant morphology and lastly the geographical situation.

Haworthia marxii in cultivation.

Anyone who propagates haworthias from seeds will know that most summer-flowering species are a bit more reluctant to produce lots of fruit and seeds. The only exceptions are H. truncata and it var maughanii. Most of the H. magnifica and H. mirabilis members tend to produce rather thin peduncles bearing fewer and more delicate flowers and fewer fruits. This is why, for example, that very few growers have problems producing and propagating seeds of the spring flowering species like H. bayeri, H. emelyae, H. mutica, H. retusa, etc. But when it comes to H. splendens, H. badia, H. maraisii and H. magnifica, few people manage to propagate them in large quantities from seed. 
 

H. marxii leaf-propagations in progress.
The reasons are numerous. In some areas the ambient air humidity during mid- summer may be too dry or too humid. In very dry areas, the Haworthia pollen simply desiccates and ‘crystallizes’ into useless granules. In areas with high summer rainfall and air humidity, the flower peduncles of many haworthias may wilt and collapse before flowers can develop. In fact, the wilting of peduncles occurs even in such a favourable climate as the Little Karoo and in the case of H. marxii more frequently than in any other summer-flowering Haworthia. The very thin peduncles are also much more prone to the fungus (?) that causes the wilting to occur. 

A painful sight every summer- a wilting peduncle of H. marxii. It remains a mystery just what kind of fungus causes this.

In the wild there are more fruit pests around during mid-summer and Haworthia fruits are a favourite of a small fruit fly that bores holes in the fruit wall and lay eggs inside the seeds.
In the South-Western Cape Province and Little Karoo mid-summer is the dry season which also means that browsing animals are more likely to eat the pregnant peduncles of haworthias. Field mice are particularly fond of Haworthia fruits.
I often said that it is a miracle that most of these summer-flowering haworthias manage to reproduce from seed in the wild with so many hindering factors.
In the case of H. marxii, all these mid-summer obstacles apply. Furthermore, the germination rate of H. marxii seeds in cultivation proved to be considerably less than those of other summer-flowering elements.
And if that is not bad enough, it has become indisputably clear that the growth rate of H. marxii seedlings is the slowest in the entire subgenus Haworthia. Seedlings sown on May 7th 2008 still measure 4 cm wide and has not reached flowering maturity after 7 years ! Seedlings of H. splendens and H. badia sown on the exact same date are now fully mature ‘old’  parent plants, flowering and producing seeds each year for the past 4 years.
Fortunately it is possible to propagate H. marxii from leaves and although it takes about a full year before the leaf starts producing offsets, they do develop a bit faster than seedlings.  
Gariep plants in Pretoria soon realized that the best way to produce H. marxii in quantity would be with the use of tissue culture. For a few years all tried and tested techniques to propagate H. marxii from tissue culture failed but finally during 2010 the tissue culture laboratory was successful.

Successful maintenance of H. marxii in cultivation is also dependent upon realizing the specific requirements of the species. Quite a few essential pointers can be obtained by studying how these plants grow in habitat.
Not only do these plants grow on relatively steep shady south slopes, but they even hide well hidden in crevices or underneath shrubs. When grown in strong light in cultivation, H. marxii will shrivel and turn brown and lose roots. To bring such a plant back to plump healthy condition is difficult and can take many months. In contrast to most other haworthias that are quick to regrow roots, H. marxii is very slow and reluctant to do so.
This shade-loving character may ironically mean that growers in areas of the northern hemisphere who normally struggle to give their plants enough light may find H. marxii quite happy in a relatively dark greenhouse.

Habitat of H. marxii. A relatively steep southern slope consisting of sandstone boulders with the plants hiding deep inside the crevices and in soil pockets amongst the rocks.


The area south of Laingsburg is transitional in more than one aspect. It is the transitional area between the Little Karoo and the Great Karoo and also the beginning of a gradual change between summer and winter rainfall areas. To the north of Laingsburg summer rainfall starts to dominate while to the south most rainfall occurs during the cooler months. Rainfall peaks occur during late fall and early spring.
Although the average rainfall in the specific mountainous habitat area of H. marxii is higher than in the very arid surrounding flats, it is still quite low, roughly between 8 inches ( 200mm) and 12 inches ( 300mm) per year.
Therefore, although water must be given very sparingly, watering throughout the year may be necessary for H. marxii. It grows near the top of the Rooiberg Mountains south of Laingsburg at 1 100 m altitude and surrounded by lots of solid rock surface. This means that the plants must surely benefit from water runoff during rainfall and even condensation on these rocks during misty weather conditions. Being on a steep slope, the drainage must also be quite significant which means the plants are never in a soggy wet situation. 
 

Mature plants of H. marxii in cultivation showing the variation in leaf patterns and dark colour despite being grown below 80% shade cloth.
Summer temperatures at 1 100 m altitude are also a bit less severe than on the lower lying areas, where it can regularly climb to over 40ºC during January to March. In addition and as mentioned, H. marxii hides well-shaded on the cooler south-facing slopes.
The minimum temperatures experienced at the specific habitat may also be less severe than in some flatter areas at that altitude. The 1100m altitude is a bit too low to receive snow during winter although it may probably happen once or twice during a century. Still, winter nights drop regularly to below freezing at that height during mid-winter and might even fall as low as minus 4 ºC. But, being situated on a slope and on a high hill-slope, it is unlikely that it may get so cold where the plants hide. I would therefore not recommend allowing H. marxii to experience temperatures below 0ºC in cultivation, probably better to keep them above 4ºC. It must also be remembered that although many haworthia populations in the wild may regularly experience 0ºC or little lower in the wild, the duration of such low temperatures is very short, only about two to three hours before sunrise and as soon as the sun rises, the temperatures rapidly climb to above freezing. Such frosty nights always occur during cloudless weather that allows such severe heat loss radiation to take place overnight but that also guarantees a sunny day to follow with a midday temperature of just above or below 20º C.

Another important factor is ventilation. It is clear that these plants demand a situation where air can flow freely and in the wild there is almost constant air movement. During a visit to the habitat Martin Scott and I tried to determine why it was that the population of H. marxii suddenly stops at a certain point westwards along the hill slope despite the fact that the habitat continues unchanged. Then we realized that at that specific point the wind breaking effect of a parallel and adjacent hill to the south-west could be felt. This suggested that H. marxii is only growing where there is direct effect from the regular and cooling south-westerly wind.

The soil mix for H. marxii should be very well drained, more so than for the average haworthia. Best results were obtained in a mix of 80% perlite with the remaining 20% being sifted leaf mould or sifted loam. Both loam and well broken down leaf compost work equally well.

Looking eastwards from the top of the hill slope where H. marxii grows.


In conclusion:
Although Haworthia marxii is not outstandingly attractive in terms of collectors appeal it must be one of the most interesting and puzzling elements within the genus. It’s unexpected and unusual geographical situation in addition to a combination of unique morphological and flower features that are not clearly linked to any known species places it in the same category as H. springbokvlakensis for example. In fact, it may be easier to justify the inclusion of H. springbokvlakensis into H. emelyae than it would make sense to attempt a forceful inclusion of H. marxii into the latter.

References:

Gildenhuys, S.D. 2007. Haworthia marxii (Asphodelaceae, Aloaceae), a new species from the Little Karoo, South Africa.  ALOE 44(1) : 4 -8.

Marx. G. 2007. The hidden mystery Haworthia of the Rooinek Pass revealed. ALOE 44(2) : 34 – 37.

Gallery with a few more Pictures:  


Branches of a shrub moved aside to reveal a large specimen of H. marxii growing below it. Note the flattened habit of the rosette.
Two plants growing together inside a narrow crevice
 

No more space for expansion. H. marxii tightly packed inside a small opening amongst the rocks. 

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