Veld & Flora Feature

THIS FEATURE IS FROM VELD & FLORA MARCH ISSUE 109 (1), PAGES 18-23

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Solving orchid puzzles

The contents of a plant pot set Dean Phillips on a trail through four provinces to pin down the identities of a baffling genus of forest orchids

JULY 7, 2023 | WRITTEN BY DEAN PHILLIPS. PHOTOGRAPHS BY HERBERT STARCKER & DEAN PHILLIPS

 

 

Solving
orchid
puzzles

Above: In bloom at the UKZN botanical garden is this surprisingly showy ‘Venus’ stenoglottis cultivar.

 

A POT PLANT RARELY looks like the gateway to a life-changing journey. But when Dr Benny Bytebier, curator of the University of KwaZulu-Natal’s Bews Herbarium in Pietermaritzburg, introduced me to a small collection of potted plants growing in the campus botanical garden, it turned out to be a decisive moment.

I was working as a research assistant at UKZN and this was the first time that I had encountered the stenoglottis, a problematic genus of small forest orchids endemic to southern and east Africa. The species within the stenoglottis genus are easily distinguished from other orchids. The problem, I found, has been sorting out the species within the genus itself.

Stenoglottis species descriptions seemed to blur together instead of pinpointing each one’s distinctive characteristics, explained Dr Bytebier. This was at least partly because they had never been comprehensively studied – and he challenged me to put this right as an MSc project.

 

Left: Anything from five to 70 blooms cascade around a stem of fringed stenoglottis. Right: Rockier crevices in partial shade are home to long-leaved stenoglottis.

 

FORAGING IN FORESTS

Applying current techniques such as DNA data could solve the confusion to update the species’ taxonomy, he believed. This included a range of approaches from microscopic comparison of the size and shape of the plants’ parts (morphology) to tracing their development and ancestry (phylogenetics).

I did not immediately realise that I would be starting from absolute basics and spend most of the next three flowering seasons scouring indigenous forests from the Eastern Cape through KwaZulu-Natal and Mpumalanga to Limpopo. I would be hoping to find these challenging little shade-loving and rock-dwelling orchids.

ENIGMATIC ORCHIDS

It was German botanical explorer Johann Franz Drège (1794-1881) who first collected a scientific specimen of this orchid genus somewhere between the Mzimvubu and Msikaba rivers on what is now the Eastern Cape Wild Coast. This was established as the species type in 1837 when English botanist John Lindley (1799-1865) of the Royal Horticultural Society botanical gardens in Chiswick, London, described it scientifically and named it Stenoglottis fimbriata or fringed stenoglottis.

This single species was all that science knew of the stenoglottis genus for more than 50 years until in 1891 Sir Joseph Hooker (1817-1911), director of the Royal Botanic Gardens, Kew, described Stenoglottis longifolia or long-leaved stenoglottis. In the decades that followed, several more species and varieties were discovered but the genus remained small, with no more than nine accepted names at any one time.

Being so small and delicate, stenoglottis flowers preserve poorly when pressed and dried for the herbarium. This has added to the difficulty of studying them from herbarium specimens.

 

Left: Fringed stenoglottis prefers to grow among mossy boulders on the forest floor. Right: Some fringed stenoglottis can have variable spotting on a rosette of leaves measuring up to 30 centimetres across.

 

Even modern DNA testing is difficult as DNA cannot be easily extracted from old stenoglottis herbarium specimens either. It was clear that if I was going to do a thorough investigation, I would need to do a fair amount of travelling. I would have to find the plants in the wild, collect fresh leaves for DNA analysis and pickle the flowers in ethanol – a more suitable method for retaining the orchid flowers’ three-dimensional structure so that I could later study size and shape differences. 

SCRAMBLING FOR SPECIMENS

And so I crisscrossed SA’s summer rainfall region – the centre of diversity of the genus – for the next three flowering seasons, searching for stenoglottis in their preferred habitats in indigenous forests. I found myself checking cracks and crevices along cliff edges, scrambling over mossy boulders, even climbing the odd tree where the plants can occasionally be found growing epiphytically.

Stenoglottis species are often found in close association with other forest understorey plants that have superficially similar flowers, particularly plectranthus. Searching for their associates first is often the best way to spot them. Ultimately, I collected specimens in four provinces from Magwa Falls in the Eastern Cape to Magoebaskloof in Limpopo and more than 50 sites in between. At the end of each trip, I was back in the phylogenetics lab to study my finds and try to sort out stenoglottis species boundaries.

Stenoglottis in your garden

Most indigenous terrestrial orchids are notoriously difficult to grow but stenoglottis
thrive in cultivation, preferring partial shade and well-drained soil. They have never
gained huge popularity in the horticultural trade but their resilience in cultivation
and attractive flowers make them good shade-house ornamentals. Several striking
cultivars have been produced.

Above: Stenoglottis macloughlinii flowers between October and February.

IN THE LAB

After many hours in the phylogenetics laboratory, and many more pulling apart and measuring flowers under the microscope, my study succeeded in revising the taxonomy of the genus. Five distinct species and one variety of stenoglottis are now recognised.

Attempting to untangle stenoglottis was my first foray into systematics research. It proved to be a challenging but rewarding experience that taught me the value of patience, a sharp eye for detail, and the importance of using a variety of methods for revising taxonomy at species level.

Ultimately, it was a combination of DNA, morphology and field observation that produced a solid conclusion and made a valuable contribution toward unravelling the mysteries of this enigmatic orchid genus.

 

Above: The delicate flowers of fringed stenoglottis are only about 15 millimetres long.

 

Sorting out stenoglottis

The name stenoglottis comes from the Greek stenos, meaning narrow, and glotta, tongue. This refers to the flower’s relatively long, flat lip (labellum) that is typical of the genus.

Other characteristic features include their inflorescences of small but numerous flowers in various shades of pink or white. Their unusual leaves are often wavy and spotted with dark brown or maroon and arranged in a rosette shape at the base of the stem.

Stenoglottis can be easily divided into two groups depending on whether a spur is present at the base of the flower lip (labellum).

Spurred stenoglottis species

The three spurred species are S. woodii, S. macloughlinii and S. inandensis. The most useful features for identifying the species are:
1. Size and shape of the spur
2. Relative width and roundness of the labellum lobes
3. Presence or absence of leaf spots
4. Geographic distribution and flowering time

• S. macloughlinii is most easily identified by its spur, which is nectar-producing, up to 3mm long and has a tapering shape with a wide base and narrow tip. The labellum lobes are wider and rounder than the other spurred species.

It is the first stenoglottis to flower (October to February) and occurs within the Pondoland centre of endemism near the border between KwaZulu-Natal and the Eastern Cape. It also tends to be the least shade-loving of all the stenoglottis species, usually occurring along the tops of forested kloofs, sometimes even on rocky outcrops in full sun.

• S. woodii is very closely related to S. macloughlinii but has only a tiny spur (0.5-1.5mm long) and does not produce nectar. It flowers later (December to March) and has a more northerly distribution – limited to the region of KwaZulu-Natal around Durban and Pietermaritzburg.

• S. inandensis has the largest spur in the genus but DNA evidence shows that it is, in fact, more closely related to the unspurred species. Its spur is as long as that of S. macloughlinii but much wider at the apex. Its labellum lobes are also longer and narrower and occasionally fringed. It is a rare species, known only from Inanda mountain, north of Durban, where it was first discovered, and one other nearby locality. It also flowers later (January to April) and its leaves may be sparsely spotted, a trait never seen in the other two spurred species.

Top: The rare Stenoglottis inandensis grows in only in a few places near Durban. Bottom: Stenoglottis typically have a relatively long lip with a variety of shapes and lobes – these are fringed stenoglottis and long-leaved stenoglottis.

Spurless stenoglottis

Only two spurless stenoglottis species are now recognised: S. fimbriata and S. longifolia.

These can be most reliably distinguished by the orientation of their floral bracts and whether or not their flowers self-pollinate.

S. fimbriata has bracts that are straight and sheathe the ovary. Its flowers consistently self-pollinate so individual flowers seldom remain open for more than a few days. This is the most widespread stenoglottis species, occurring from the Eastern Cape all the way to the highlands of southern Tanzania. The species S. fimbriata now includes a previously recognised species, S. zambesiaca, as well as S. fimbriata var. saxicola and S. modesta which has been reduced to a variety.

Leaf spotting in S. fimbriata – and in S. longifolia – is extremely variable but in S. fimbriata var. modesta the leaves are never spotted and tend to be broader and fleshier, without wavy edges. This variety also has what appears to be a minute vestige of a spur at the base of the labellum.

S. longifolia has bracts that curl outwards away from the ovary and, unlike S. fimbriata, its flowers never self-pollinate. They also remain open for much longer. It is known only from a handful of localities in KwaZulu-Natal, Eswatini and Mozambique. One previously recognised species, S. molweniensis, is now considered a synonym of S. longifolia.

Above: The existence and size of a spur to the flower is a key factor in distinguishing species – these are spurred Stenoglottis macloughlinii and spurless long-leaved stenoglottis.

This study was supported by the Botanical Education Trust.

Dean Phillips (dean.phillips@uct.ac.za) is assistant curator of the Bolus Herbarium, University of Cape Town.

This article was featured in Veld & Flora in the March 2023 edition.

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