Gazania: diversification vs. speciation

The studies on Gazania by Seranne Howis are a reminder that biodiversity can’t always be divided into discrete species. Speciation may form the kind of clearly articulated branching pattern that cladists like when evolution is driven by new niches becoming available one by one. But the sudden landscape-wide diversification of a clade and its sorting by natural selection into stable entities are separate, and almost contradictory, processes – rather like an explosion and the subsequent settling of the debris. Such explosions of diversity have occurred in the Mediterranean climate zones of south-western Australia and in South Africa, as part of wholesale vegetation changes caused by the cyclical climate changes of the last few million years. Many genera were reduced to small populations in refugia during the dry periods, and rapidly diversified again in the wet periods.

The South African biodiversity hotspot has given the world several genera of ornamental plants that have been evolving in this way. Some of them are real gifts to the plant breeder because in cultivation they function as coenospecies with all their genetic diversity available for use in hybridisation. For example, Watsonia (Iridaceae) has been divided into 52 morphological species that rarely hybridise in the wild as the flowers of sympatric populations have diversified to utilise different pollinators. But they all have the same chromosome number, and can all be interbred in cultivation with the F1 generation often showing hybrid vigour and high fertility. My ‘gut feeling’ from working with Watsonia is that it’s a genus with little evolutionary depth, all the species having similar genetic architecture and closely homologous genes. Gazania is another example, in which the process of speciation may not have proceeded even as far as it has in Watsonia.

Howis showed that Gazania includes seven valid, monophyletic species – each reproductively isolated, with a distinct morphology, habitat and genetic identity – but it has the majority of its diversity in a broad complex where morphological, ecological and genetic variation are only partially correlated. The complex may be called an ochlospecies, defined as a polymorphic species with chaotic infraspecific variation intractable to formal taxonomic treatment. In her 2007 thesis, Howis tentatively called this ochlospecies by the earliest published name, G. rigens (L.)Gaertn. But Howis et al. (2009) take a more conservative course by calling it the K-R complex – possibly because G. rigens is usually applied to the stoloniferous sand-binding forms that are distinct from the others morphologically and ecologically, but not genetically.

Another model for understanding genera like Gazania might be found in Vavilov’s theory of homologous variation, which is closely related to Nabokov’s concept of homopsis. A complex that has diversified only since the Pleistocene is likely to consist of populations with similar functioning genes that determine the morphology and physiology of individual plants. This is quite apart from the fine variations in the four non-coding chloroplast sequences and two nuclear spacers used in Howis’ study. The model predicts that similar traits of morphology and physiology would appear repeatedly in response to the appropriate environmental conditions. Homopsis is a type of homoplasy in which the phenotypic similarities are due to underlying genetic similarity, instead of being due to convergence from more diverse ancestors; this would be the case with the stoloniferous ‘rigens’ forms of Gazania that do not form a genetically coherent entity since natural selection has shaped them from the same gene pool as the rest of the complex.

The many forms of Gazania introduced to Australia, and now feral here, are all within the K-R complex. For practical purposes such as gardening books and legal declaration as weeds, a Latin binomial may be demanded. There are three possibilities:

  1. refer simply to the genus Gazania. As none of the seven distinct species are naturalised here, in practice this would mean the K-R complex.
  2. use the name Gazania rigens (L.)Gaertn. to signify the whole K-R complex. This species epithet has priority under the Code, having been published as Gorteria rigens L. in 1763.
  3. separate G. rigens out as the name of the stoloniferous forms that have been planted for sand stabilisation on our coasts. The earliest valid name for the residue of the K-R complex would then be Gazania rigida (Burm.f.)Roessler. This would be similar to the treatment in the 1986 Flora of South Australia, but with G. rigida replacing the later synonym G. linearis.

References

Howis, S. (2007) A taxonomic revision of the southern African endemic genus Gazania (Asteraceae) based on morphometric, genetic and phylogeographic data. Ph.D thesis, Rhodes University Botany Department. 293 pp.

Howis, S., Barker N.P. & Mucina, L. (2009) Globally grown, but poorly known: species limits and biogeography of Gazania Gaertn. (Asteraceae) inferred from chloroplast and nuclear DNA sequence data. Taxon 58(3): 871–882.

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A Cronin Watsonia cultivar

Another old Watsonia cultivar that in my collection is labelled simply as accession 84 is in flower now, with narowly conical pink flowers that hang down like miniature foxgloves. These are unlike any wild Watsonia species, and are not well-adapted for pollination either by insects or by birds.

This is a quite distinct clonal cultivar, and is known to be one of those bred by John Cronin at the Royal Botanic Garden, Melbourne, before 1925. Its identity may never be confirmed, but the most likely candidate is Watsonia ‘Queenstown’ which was decribed as dwarf, lilac mauve (Warner, 1926). The long perianth tube and pendulous flowers, as well as the shape of the floral bracts, point to Watsonia aletroides as one parent. Some of my own hybrids from W. aletroides crossed with forms of W. borbonica or other Cronin hybrids have a similar flower shape.

Description

Medium size perennial, to 130 cm tall, dormant in summer and flowering in spring. Basal leaves 4 -5, to 75 cm long, 33 mm wide, with thin pale green margins. Stem leaves 2. Flowers 18-28 (to 5-6 open at once) on a purplish and glaucous axis plus 1-3 branches. Bract 22-29 mm long, slightly exceeding internode, herbaceous with maroon scarious apical third, dark band and scarious tip, acute to subacuminate, keeled. Bracteole shorter. Perianth warm pink in bud, opening light cool pink [FFB9D0], paling to RHS 73C [FFD5E0] on the inner lobes, deeper and warmer pink RHS 67D [FF85A1] on exterior of lower tube. Perianth tube 45 mm long, the narrow basal part 15 mm long, to 3 mm wide, sharply curved; distal part narrow funnel-shaped, pendulous, 26-29 mm long, 8-9 mm wide at mouth. Outer lobes oblanceolate, apiculate or subacute, 21-22 mm long, 10 mm wide; inner lobes oblong, obtuse, 22-24 mm long, 12-14 mm wide. Anthers below style but facing down, 9-10 mm long, purple with pale purple pollen. Style 6-branched, exceeding anthers and ultimately exserted from the corolla, pale pink. Capsule fusiform, incurved, acute, to 24 mm long. Seeds with 2 short wings, 10-11 mm long, pale brown.

Provenance – gift from Will Ashburner of Hancock’s Daffodil Farm, (his accession number 970518) in March 2000.

Reference

Warner, W.R. (1926) Advertisement in The Australian Garden Lover 1: 392.


Definitions in taxonomy

There are four ways of defining a term or a datum (Hubbard, 1951). The most obvious might be by description, or listing its essential characteristics. Then something can also be defined by its differences from similar things with which it might be confused, or conversely by classifying or associating it with things that it resembles. But the most useful is an action definition that specifies the cause and function of the thing.

This is very relevant to biological taxonomy, which is concerned with defining taxa as relatively stable entities within the diversity of living organisms.

Traditional taxonomic literature uses descriptive definitions (full description with reference to a type specimen) to establish taxa. It also uses differentiative definitions (diagnoses and keys) as tools for identification. In practice, differentiation becomes definition by elimination, as in the dichotomous keys used in floras and monographs to narrow down the possible identity of a specimen to a single name by gradient steps.

Associative definitions may also be used in the protologue to discuss the relationships of a new taxon. Association was implicit in Aristotle’s concepts of genus and species, which Linnaeus adopted in the binomial nomenclature of plants and animals. Thus placing a new kind of cat into the genus Felis is a starting point for defining it. But an associative definition depends on the user’s prior knowledge of the thing being associated. It’s little use describing a lynx as a cat with certain characteristics to someone who has never seen any cats.

An action definition of a species would include its origin (the genus within which it evolved), its niche (functional role in the ecosystems where it lives), and its limits. e.g. “Watsonia hysterantha is a local derivative of W. meriana flowering in autumn from stored reserves, reduced in size and ground cover to exploit soil pockets in granite cliffs.”

An action definition of a higher taxon would similarly include its origin from a taxon of similar rank or the next higher taxon to which it belongs, the functional adaptations that caused this line to diverge, and its limits. e.g. “Cactaceae are caryophyllids adapted to seasonal drought by crassulacean acid metabolism and water-storing stems, with consequent slow growth rates making them vulnerable to competition”.

A species is a solution to the problems posed by its niche and environment. It is the lowest level taxon that can be called stable in that it is not liable to vanish within a few generations due to gene flow. There is no guarantee that a morphological species, based on museum specimens of distinctive appearance, has such stability. For practical purposes a taxonomic species is often taken as equivalent to a biological species: a reproductively isolated population or group of populations. The biological species concept was adopted by zoologists who considered only sexually reproducing organisms and ignored such things as clones and apomicts. But sterile or apomictic clones are morphologically distinct and function as species in ecology even though they do not fulfil the biological definition of a population as a unit within which genes are exchanged.

Like a key that fits a lock it wasn’t meant for, a species may fortuitously fit another environment quite different to the one where it evolved, as when an introduced crop species unexpectedly becomes a weed. But a population moved to a new habitat immediately becomes a new biological species because it is reproductively isolated from the original population and subjected to different selection pressures. Morphological changes may occur later, but it has already started on a new evolutionary trajectory. Bulbil watsonia is an example, a vegetatively reproducing biotype of Watsonia meriana that was reproductively isolated by becoming triploid and found a niche in habitats disturbed by human activity, first in its native South Africa and later overseas.

Reference

Hubbard, L. Ron (1951) Advanced Procedure and Axioms.


Kroy’s insight

In a little-read paper from 1977, the philosopher Moshe Kroy almost casually expressed an insight that I find breathtakingly daring. Apart from its political significance, it has implications for taxonomy – which is why I’m including it in this blog – and for many other things as well. Kroy was analysing a seemingly trivial disagreement between two schools of Libertarians represented by Ayn Rand and Murray Rothbard to reveal its deeper roots. He resolved it by recognising that the problem only arose from the assumption made by Rand and many 20th century philosophers that individual humans are deterministic entities within the deterministic system that we call Community or Society. He wrote:

“Actually, within a deterministic context, any concept of entity as an ultimately discrete existent loses all significance. All entities easily reduce to parts of larger systems”.

“Only the stress on the individual as ultimately free establishes his individuality – being a distinct first cause.”

Entities are anything that we postulate and identify as complete units, separate from other such units. They range from planets to atoms, with our own bodies and the objects we use in daily life somewhere in the middle of that spectrum. The mental life of humans is all about perceiving entities in the world around us, understanding how those entities interact and using them to achieve our purposes. But the entities that we perceive in the universe of matter, energy, space and time are little more than convenient fictions. They reduce to parts of larger systems because they all ultimately have a common origin and are part of one big ‘machine’.

Taxonomists are concerned with organisms that are all products of a single evolutionary process from a common origin: the evolution of Earth’s biota, however many billion years it has taken, is a single event. No plant or animal is an individual since it has organic continuity with its ancestors and its siblings. Nor do species, genera and other taxa exist objectively as irreducible entities. At best, these are working hypotheses, useful divisions of the diversity that exists within biota. It is not surprising that taxonomists continue to have differing opinions on the extent to which some genus should be divided into species. The boundaries drawn between taxa may legitimately depend on the purpose of the classification.

In this paper, Kroy is concerned with the political freedoms of human beings, and he rightly saw that these freedoms have no theoretical basis as long as we consider people merely as physical entities in a deterministic system. On the other hand, each person – as distinct from the material body, the organism they temporarily inhabit – is a true individual. We are not products of evolution, or creations of some occult power, but are each the first cause of our own existence.

Kroy’s second paragraph demonstrates the influence of L. Ron Hubbard on his thought. He had encountered Scientology in his native Israel, and during 1976 was studying at Melbourne’s Church of Scientology while also lecturing in the Department of Philosophy at La Trobe University, but later diverged to follow his own intellectual path.

In a long footnote Kroy attributed this insight to Spinoza, who argued from an assumption of determinism in the Ethics that only one self-existent substance (substantium in the old scholastic sense) could exist in a universe, since everything else in that universe would be contingent on that substance. But it took a 20th century Libertarian to see the implications of Spinoza’s statement.

Reference

Kroy, M. (1977) Political freedom and its roots in metaphysics. Journal of Libertarian Studies 1(3): 205-213.


The saxophone watsonia

There’s a peculiar Watsonia cultivar that has been around in Australia for a century or more, but whose origin is unknown. Those who speak of it at all call it the saxophone watsonia because the flowering stems become curved down and then up again in their development, forming a J-curve like the tube of an alto or tenor saxophone.

Description

A perennial, dormant in summer and flowering in spring. Corm flattened, to 5.5 cm diam. Basal leaves 3-4, to 47 mm wide, non-glaucous green with thickened brownish margins. Stem leaves much smaller. Flowers begin in early October. Spike J-curved, with numerous short branches. Bract peracute, scarious with a green base, 20-24 mm long, exceeding internode. Bracteole shorter, bifid. Perianth mauve-pink. Tube 15-24 mm long; basal part 10-15 mm, distal part funnel-shaped, 5-9 mm. Lobes elliptic, obtuse, usually apiculate; no callus or mark at base. Outer ones oblanceolate, 26-29 mm long, 12-14 mm wide; inner obovate, 28-32 mm long, 15-16 mm wide with slightly undulate margins. Due to crowding, lobes may depart from normal aestivation with some inner lobes overlapping the outer. Stamens equilateral. Seeds very shortly 2-winged, 9-10 mm long, pale brown.

Named cultivars of perennials like watsonia are normally clones, but the saxophone watsonia is a line consisting of at least two genotypes. I have two accessions that have shown consistent phenotypic differences when grown side by side over 13 years.

  • Smaller plant (accession 34): Leaves to 63 cm long. Perianth mauve-pink, RHS 75A; tube 14-17 mm long. Anthers 9-10 mm long, dull yellow. Style branches equal or exceeding stamens. Capsule cylindrical, obtuse, 13-16 mm long. Provenance – a fete at St Jude’s Anglican Church, Brighton SA.
  • Larger plant (accession 35): Leaves to 79 cm long. Perianth a slightly cooler and darker mauve-pink, RHS 74D; tube 18-24 mm long. Anthers 12 mm long, purple. Style shorter than stamens, spreading between them. Capsule broad-fusiform, acute, 16-18 mm long. Provenance – Reids’ Nursery, Wodonga.

Judging from its leaf and flower characters, saxophone watsonia is a derivative of W. marginata, which often produces distorted flowering spikes in the wild. The other parent is likely to have been W. borbonica. I haven’t found it easy to use W. marginata as either parent in hybridisation, but the existence of the saxophone watsonia implies that such crosses can occur.

The Watsonia ‘Curviflora’ mentioned by Pescott (1926) may possibly be this plant; he noted that it had light magenta flowers on a stem “curved laterally”, and that it was bred in Australia. This name had been published as a nomen nudum by Schomburgk (1871), but with a question mark and was dropped from his next Botanic Garden catalogue in 1878.

References

Pescott, E.E. (1926) Bulb Growing in Australia. (Whitcombe & Tombs: Melbourne).

Schomburgk, R. (1871) Catalogue of Plants under Cultivation in the Government Botanic Garden, Adelaide, South Australia. (Government Printer: Adelaide).


Nabokov’s taxonomy

Many thanks to Dieter Zimmer for making his fascinating work A Guide to Nabokov’s Butterflies and Moths available to all readers online. This Web Book is particularly valuable as the original publication is already out-of-print and rare.

This book identifies all the butterflies and moths mentioned in Vladimir Nabokov’s scientific papers and his fiction: not a simple cataloguing job, since their nomenclature has changed repeatedly both during and since Nabokov’s time. As well as being an illustrated taxonomic reference work, it includes a concordance of the many references to Lepidoptera in his novels, poems and stories. It also lists the species named by Nabokov, and those named after himself, his family and characters in his fiction. But in my opinion the most interesting section is the treatment of Nabokov’s concept of the species and his views on evolution.

Vladimir Nabokov had abilities that are often associated with autism. His synaesthesia was well documented and was evident in his literary style. So was his eidetic ability to recall and cross-reference large numbers of mental images. In The Real Life of Sebastian Knight he wrote convincingly of how it feels to live in ‘constant wakefulness’ with every impression provoking a multitude of associative ideas. If there were such a thing as an aspie approach to taxonomy, the works of Nabokov might contain some clues to its nature.

While most zoologists were following the Neodarwinist fashion of downplaying morphological evidence and defining biological species based on observed or supposed limits to gene flow, Nabokov defined species on morphology and regarded biological data as secondary. Since he emphasised the morphology of the insects’ genitalia, the boundaries of his morphological species tended to coincide well with the practical limits to interbreeding of sympatric species in the field. He agreed that natural selection was the cause of an organism’s adaptation to its niche and habitat. But he remained sceptical of natural selection as the sole cause of the evolution of morphology of organisms and in particular the very widespread phenomenon of homoplasy (the evolution of similar characters in different clades and species).

Convergence was the old term for one kind of homoplasy: the independent development of similar but possibly superficial characters in widely separate clades. Nabokov understood that this phenomenon must be rare due to the number of genes involved and the statistical improbability of enough mutations with phenotypic effects in the right direction becoming fixed in a taxon. He introduced the new word homopsis for a more usual form of homoplasy: the repetition of characters in related species, due to similar sets of variations appearing in species with a similar genetic basis. This concept can be compared with homologous variation as conceived by the botanist Nicolai Vavilov – a Russian contemporary of Nabokov. Ever the synaesthete, Nabokov described a pattern of variation among species that contained gaps as a syncopated or jerky variational rhythm. For example, if two closely related moths had melanic variants and a third did not, this was an anomaly that called for an explanation.

In the 18th century Linnaeus considered genera to be more real than the species (literally, ‘appearances’) into which they could be divided. But in our time the genus has become an even more slippery concept than the species in biological nomenclature. Nabokov noted the limitations of Linnaeus’ binomial system where, following Aristotle, every species must belong to a genus. A genus of several species is defined by a particular combination of morphological characters that are common to them all. But a single-species genus has no reality beyond the implication that a common character combination would be revealed if some hypothetical, related species were to be found. Genus, species, and all taxonomic categories are noumena rather than phenomena. They exist only as mental constructs by which humans try to impose order on the kaleidoscopic variety of the world.

Many of Nabokov’s novels, and above all Pale Fire, are concerned with questions of identity. I suggest this is a key aspie characteristic: we’re so aware of everything around us that we sometimes have to think twice to find the boundary between self and not-self. Taxonomy is also concerned with postulating discrete entities among the continuous variation of organisms and drawing boundaries that identify them. It’s a branch of science that might have a natural appeal to aspies, as it did to Nabokov who took his first Cambridge degree in zoology, and later while a Lecturer in comparative literature at Harvard would work for up to ten hours per day on the Lepidoptera collection.

References

Nabokov, V. (1944) Notes on the morphology of the genus Lycaeides (Lycaenidae, Lepidoptera). Psyche 51: 104-138.

Nabokov, V. (1945) Notes on the Neotropical Plebejinae (Lycaenidae, Lepidoptera). Psyche 52: 1-61

Vavilov, N. I. (1922) The law of homologous series in variation. Journal of Genetics 12: 47-89.

Zimmer, D.E. (2001-2003) A Guide to Nabokov’s Butterflies and Moths. 438 pp. ISBN 3-00-007609-3


Five ways of knowing

We all start out with assumptions that a few concepts are supposed to be self-evident. At first, basic English words like ‘self’ or ‘think’ or ‘know’ might not seem to need any definition or explanation. But as we get older we may find that not everyone understands these concepts in the same way.

Knowing is the English word from the same root as the Greek gnosis or the Sanskrit jñāna. Awareness, understanding, and even intelligence are close to being synonyms.

At the lowest level, facts stored in memory might be called knowledge. But a computer can’t be said to know anything, however much data is stored on its hard drive. Knowing presupposes that there’s someone there capable of being aware. And it’s possible to know without memory, as when one first has an experience before verbalising it or storing it in memory. Then there’s another way of knowing that is variously called mental modelling, visualising or imagining.

One model of the possible ways of knowing was devised by the Tantric branch of Buddhism about twelve centuries ago. They settled for a five-way classification, with the five jñāna (five wisdoms or knowledges) corresponding to the five elements into which the Buddha and his first followers had deconstructed the subjective experience of selfhood. Their terminology remains useful as long as English lacks rigorous definitions in this area.

  1. Analytical intelligence, recognising the differences between things and solving problems by breaking them down into their components. The Tantrics called this by the Sanskrit word pratyavekṣaṇajñāna. This process includes deduction as defined in formal logic, reasoning from the general to the specific and making predictions about concrete instances from general rules that have been previously established.
  2. Complementary to pratyavekṣaṇajñāna is the ability to recognise the similarities of things and group them into larger wholes. This is samatājñāna, which corresponds to classification or induction as it enables us to reason from the specific to the general, and induce concepts from observations or concrete examples.
  3. Let’s not forget practical intelligence or kṛtyanuṣṭhānajñāna. This has nothing to do with conceptualising, much less with verbalising, but rather with conscious action to accomplish the desired result. But it’s surely a form of intelligence: for example, the skill that an experienced musician develops in their hands. Instead of having to look for the next note to play as a beginner would, they go directly from the sound they have in mind to the necessary movement of their fingers.
  4. I’ve named this blog after the fourth kind of knowledge, ādarśajñāna. The literal meaning of this term, “mirror knowledge”, is a good metaphor, except that mirrors reverse right and left, and ādarśajñāna doesn’t make even this much alteration. It is awareness reflecting the thing observed, in its entirety, prior to any analysis or classification. Scientologists call it duplication, i.e. copying a datum or an action exactly.
  5. But the highest method of knowing is to simply be the thing you want to know. This is what the Tantrics called tathatājñāna, literally “knowledge of suchness”. While the other four might be called processes through which we gain knowledge, the fifth is the end goal where any distinction between an object of knowledge and its reflection in our awareness disappears. In Scientology this is called as-is-ness. At this point we truly know a thing inside and out, can use it, but don’t have to carry it around as a mental picture anymore.