The Haworthia pollinator

While I have seen and recorded a Solitary Bee species pollinating the flowers of Haworthia, I have never succeeded in photographing it.  Slightly larger than the ordinary Honey Bee, it is a very rapid and busy flyer and does not spend time at any one flower.  Here in Cape Town it is relatively rare and there has been an odd season where I have not seen it at all.  It makes a nest consisting of a short tunnel dug into the ground where it makes a series of nectar and pollen filled cells in which the eggs are laid.  At Worcester these insects were very common and on one occasion I came across them nesting in large numbers in a small patch of bare gravelly clay.  It is remarkable how they were obviously able to recognize and home in on their own small tunnels.  It does come into relatively insect proof enclosures and can make isolation of plants for pollination difficult.  It is unlikely that flying distance has been measured and it seems very unlikely that it will match the observed maximum of the Honey Bee at 13km (8miles).  However, I do not know the length of the life cycle and the relation of the feeding/foraging activity to its nesting behavior.  It may be possible that feeding but non-nesting bees disperse over greater distances.

The chance to take the two photographs presented here came quite by chance.  I was in my plant house that is partly accessible to insects, and saw the bee on a Haworthia flower stalk.  Its jaws were clamped on the peduncle and it was totally stationary.  I took a few pictures and then attempted one from another angle.  In doing so I had to dislodge a second peduncle from nearly under the bee.  The slight difficulty in doing so did not register properly.  I took a picture and then suddenly the bee came to life and flew off to resume foraging in the house.  But it soon settled on another inflorescence (on a plant at another table) again on the peduncle with its jaws clamped on the talk as before.   I removed some pollen coated threads hanging from its back legs and left.  While downloading the pictures I saw that I had photographed a spider on the peduncle under the bee in my second angle.  So went back to see.  The bee was still stationary on the flower and then I saw what I thought was the same spider crawling over the bee.  Somehow I disturbed the bee again and it flew off up into the shade cloth in seemingly healthy fashion.  The next day I thought I would check the original peduncle to see if there was any web.  Much to my surprise I saw the original spider and no web.  I have seen these small yellowish spiders on flowers before and also noted small amounts of web.  Very occasionally there have been dead flies sitting attached to the flower stalks but not with any noticeable web.

So it is still a bit of a mystery if this small spider, or spider pair, could actually capture and immobilize such a bigger potential prey.  Certainly the bee I observed had encountered web and may have grasped the stalk to free its hind legs to work the web off.  I did not observe anything more than minimal movement to do so.

Regarding pollination.  I was not doing any controlled pollination during which I would have been checking for the presence and exclusion of the bee.  But what I did observe was seed set on H. limifolia clones that I could not achieve although in desperation I have transferred pollen between different collections.  The bee had an advantage in also bringing pollen from unrelated species.  This was on H. limifolia ‘gigantea’ and on H. limifolia ‘glaucophylla’.  While I have set a few capsules on the former, I have achieved none on the latter.  What is interesting is that no seed was set on field collected clones of H. limifolia presumably ‘keithii’ from Isiteki.

During feeding/foraging, the bee holds onto the lower flower limbs and very briefly inserts its ‘tongue’ into the flower and buzzes away.  I could not see any deliberate hovering and pollen transfer to the back legs as does the Honey Bee.  But pollen is collected and carried in approximately the same way.  When I hand-pollinate I adopt the simple approach of approximating the insertion of hair (bees ‘tongue’) into one flower to obtain pollen and then into another to deposit it.  Better results are claimed for physically exposing the stigma and transferring pollen using a brush.

A recent trip to photograph flowers resulted in us finding H. floribunda southeast of the Bontebok Park at Swellendam.  I have reported elsewhere that I had seen this species within the park but repeated visits had turned up nothing but similar looking H. mirabilis.  On this occasion we were outside the park where we have recorded H. mutica, H. marginata, H. minima, and also similar small forms of H. mirabilis as occur inside the park.  We explored a small area we had not covered before and were delighted to find H. floribunda, now easy to see because they were in flower.  However, we proceeded to the H. mirabilis locality and on the way again found H. floribunda that we had missed on the previous visit.  We also found more H. mirabilis about 60m further along and still about 100m away from the original H. mirabilis locality.  These four species were along a stretch of about 5-600m and not occupying shared habitat.  The vegetation was fynbos on shallow alluvium, quite stony and well-drained.

It was while photographing the flowers of H. floribunda that a furry fly appeared and ignoring us and the camera, attended to the flowers.  While I was trying to get a picture of this fairly fast moving fly, the Anthophorid bee pollinator also appeared but flyng too fast and haphazardly to be pictured.  We had seen the same fly on H. mutica at the Buffeljags habitat.  The species is Australoechis hirtus known to be a pollinator and visitor to many flower kinds.  The flies are nectar feeders and parasitize other insects in their reproductive process.

While we do not know what the pollinating effectiveness of these insects over distance is, it is quite obvious that in this situation there must be substantial transfer of pollen across all the species given the short distances involved.  Three of the species were in flower.  But H. marginata, curiously, at this locality flowers nearly 5 months earlier than at other known places.  Despite that, there are hybrids with H. minima.  There did not seem to be hybrids among the H. floribunda plants, but we did think that some of the plants of H. mirabilis could have been hybrid.

Note the white spider.

Unbusy bee

Australoechus hirtus on H. mutica. Rotterdam.

Australoechus hirtus on H. mutica. Rotterdam.

 

Haworthia flowers – some comments as a character source, part 1

Haworthia flowers – some comments as a character source.

M B Bayer, PO Box 960, Kuilsriver 7579, RSA

Introduction:

The object of this essay is to discuss where we are now with respect to classification of Haworthia. Despite my comments and observations stretching over 50 years, there are still taxonomists writing and arguing on the basis of method and practice that generated the anarchy of names that existed at the start of my involvement. This method is what is probably referred to as “typological” i.e. there is a single herbarium specimen and anything that departs from this in some mind catching way is a different and thus needs a new name. At the generic level, recent DNA studies show that Haworthia is indeed three separate entities (the subgenera), and that these cannot be rationally separated from the aloid genera. Formal classification requires that Haworthia thus be subsumed in Aloe (see Treutlein et al, Rhamdani et al and Daru et al). This is both incomprehensible and anathema to writers and collectors locked into method that does not rest on any insight to what the problem of species actually is, let alone take proper cognizance of the problems that exists at generic level.

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Haworthia flowers – some comments as a character source, part 2

 

2. THE RACEME. Figures Set 2 show the bases of the peduncles in several collections to again show how variable they are and not only because of plant vigor and current growth conditions. Diameter can vary by a factor of three. Color is variable and the bract spacing and size of bracts as variables must be noted. Fig 6 is simply a robust spike in a population where the flowers were sparsely spaced on the stem with approximately 15-20 flowers per stem, whereas this raceme had nearly 30 flowers. The number can drop to as low as three. In 7917 we noted a single plant with an inflorescence of over 600mm where the average was below 300. Similarly at 7818 there was one colossal inflorescence of 800mm where again the average was between 300 and 400mm. There is a real problem in that the typological attitude is often adopted when making comparisons like this. An extreme example would be to take H. retusa south of Riversdale as typical of the species. These are massive plants (source of ‘Jolly Green Giant’) and the inflorescences are huge with many flowers. This is not typical for the species and especially so if one takes the mountain cliff populations (H. turgida) to be the same species (as I do) where the plants are proliferous and the inflorescences many and reduced. Plants in poor niches and even poor habitats, flower weakly and the inflorescences are reduced. Figs 7 shows varying capsule positions on the stem. Figs 8 and 9 show a distichous and a secund inflorescence and figs 10 to 15 demonstrate the varied spacing of the flowers that is observable even in any one population although the images are for two different accessions. In Fig. 8 the middle flowers are in a single plane and I regret not having observed the leaf arrangement in that specific plant, because this is a distichous arrangement as the low Fibonacci number of a spiral arrangement of the flowers. This may have been reflected in the leaf arrangement too. The spacing and arrangement of the flowers is also a variable and the number of flowers may also vary. Figs 16 to 18 show bud arrangement and the way in which the fish-tail buds have upturned tips. Although the peduncle does continue to lengthen, most of the lengthening takes place in the flower producing area and towards the upper end of the raceme. The peduncle does not always stay straight and may bend slightly at each floret. The number and distance of the flowers along the peduncle may affect bud packing just as peduncle formation in the rosette results in the appearance of a groove on the leaf face. This is a secondary physical phenomenon and is not an inherent “character”. The leaf keel for example may also be influenced just by physical leaf-packing. A peduncle of a flower from the centre of a plant will have a many angled base, but one arising from a leaf axel only 2-angled. Generally the raceme is indeterminate, meaning that it does not end in a pedicel and flower. But I have seen an individual raceme of H. floribunda with a terminal flower. This exemplifies our problem where characters one might think could be used to determine even genera, are variables at species level.

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Haworthia flowers – some comments as a character source, part 3

 

6. THE CAPSULES. Figs 6.1 first size differences that can be found within individual inflorescences. The remaining images show 8 capsules per population for a few populations to show variation in size and shape. The way the capsule ripens and splits is very variable. In some cases the capsule is pinched near the end but the locule tips flare outwards. This has the effect of seeds being retained in the capsule. In others the locules flare regularly and symmetrically from the base and the seed is all easily released. In the Van Reenen Crest populations the capsules were inclined to be a reddish hue. But colour can vary depending on the ripening process and they also bleach with time. Fig.6.4 7978 shows this in capsules drying after the peduncle was taken, and retaining their greenish colour. In H. floribunda the capsules are smaller and it appears that they may flare at the tips more in splitting and be coarsely crispate. This is not always the case but it is a tendency in the smaller capsules to do this. Fig. 6.7 is of capsules in 7910 H. floribunda, Rietkuil; compared against 7913 H. mirabilis also Rietkuil east of Swellendam. It is quite evident that even a capsule structure as apparently characteristic as in H. floribunda, is replicated in a different species. Fig. 6.8 is of 7955 Van Reenens Crest, and 7262 south of Greyton. I thought the capsules of 7955 were smaller, reddish coloured and slightly rougher than those of 7262. But the capsule structure in the entire genus is very similar to those shown on this figure and it is just not conceivable that some feature will stand out and resolve issues that exist in respect of the entire group.

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New finds in Haworthia.

Previously published Cact. Succ. J. (Los Angeles) 84(1): 41-50

Map - east of Swellendam

 

Map Legend – east of Swellendam.
1. JDV84/75 Haworthia retusa ‘turgida’.
2. MBB6666 H. retusa ‘nigra’↔ H. mirabilis.
3. MBB7898 H. retusa ‘nigra’.
4. MBB7899 H. retusa ‘nigra’.
5. MBB7897 H. retusa ‘nigra’.
6. MBB7896 H. retusa ‘nigra’.
7. MBB7871 H. mirabilis.
8. MBB7823 H. mirabilis.
9. MBB7909 H. mirabilis
10. MBB7805 H. mirabilis.
11. MBB7801 H. mutica ‘groenewaldii’.
12. MBB7886-7889 H. mutica ‘groenewaldii’, H. mirabilis, H. minima, H. marginata.
13. MBB7722 H. floribunda ‘major’

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