Eulophia petersii

Eulophia petersii
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Monocots
Order:	Asparagales
Family:	Orchidaceae
Subfamily:	Epidendroideae
Tribe:	Cymbidieae
Subtribe:	Cyrtopodiinae
Alliance:	Eulophia
Genus:	Eulophia
Species:	E. petersii

Eulophia petersii is a species of flowering plant in the Orchidaceae family. It is found in arid environments along the Eastern Coast of Africa and the Arabian Peninsula, with significant populations in the Northern Frontier Province, Kenya, the Arabian Peninsula, and the former Transvaal region of South Africa. Eulophia petersii is an unusual member of the orchid family in that it lives in a harsh desert-like environment. It is often found growing in acidic sandy soils or in rock outcroppings. The leaves of the orchid resemble those of Agaves and are 40 cm long. There are usually two to five leaves per plant. The pseudobulbs are yellow with a pronounced ribbing and 30 cm long with a diameter of 3–4 cm. The flowers are widely spaced on a 2 m inflorescence that can sometimes be branched. The flowers themselves are green with a wrinkled white lip. There is quite a bit of variability in the flowers coloration between plants. Sometimes the sepals and petals can be circinnate.

Biology

Eulophia Petersii in habitat growing between rocks.

This species appears to be pollinated by several families of long-lived winged desert beetles in the families Cetoniinae, Scarabaeidae and Elatyridae. Bees of the families Anthophorinae and Apidae (or halictid (Halictidae) bees) have been observed to visit the flower nectaries as well but have not been observed to have the pollenaria attached to them when they exit the flower. This species appears to be pollinated exclusively by desert beetles and its pollinator specificity resulted in its adaptation over time to desert-like environments. It is an unusual and unique species based on its xerophytic adaptations, which are quite rare in the orchid family, and the plants adapt and thrive in cultivation in conditions which are not as harsh as found in their native habitat. However, in the wild these plants are confined by distribution to harsh desert-like regions where their specific pollinators seem to exist, and do not seem to display native population distribution outside these areas.

Little is known about the germination and early development of these plants in the arid environments in which they live since all orchids, including this species, are dependent on mycorhizzial fungi during the early stages of orchid development for germination and protocorm formation. The current theory is based on where the plants are found in habitat. These plants are typically found in habitat growing in cracks between rocks where these cracks tend to catch windbown organic materials, including the dust-like seeds of this species. It is currently believed these plants germinate in rock cracks which can support a humid micro-climate from stored moisture beneath rocks for protocorm formation and spend only a very short period as a saprophyte before forming a burrowing stem then rapidly developing leaves and photosynthesis, a behavior observed in flask culture with this species, however, no juvenile plants in the saprophytic stage have been located in habitat to study to date that can be reliably identified as this species. This species is also one of the few that can be easily grown from seed without sterile culture or reliance on the plants native habitat, as the seeds can simply be sown on moist organic soil and will germinate and grow into mature plants outside of sterile conditions.

Although plants are at times found growing in the open on acidic sands, it is not believed these plants germinated at these locations as this species does have a 'weedy' habit and is easily propagated from cuttings and broken rhizome sections, and in some areas of Africa forming fairly large stands of plants many of which are intermixed clones of multiple parent plants. The plants are infrequently predated on in habitat by small canids and other small mammals in search of moisture. Canids tend to rip up sections of rhizome and chew off the pseudobulbs and discard the astringent, woody rhizomes, other mammals chew on the upper sections of the pseudobulbs in habitat and 'girdle' them causing the leaves to drop or dehise. It is believed that plants found in open areas away from rocks are the result of vegetative propagation by predation on the plants for moisture and the plants likely did not germinate at these locations.

Cultivation

Eulophia Petersii in Cultivation. Plants grown in conditions outside their harsh, native environment are very robust and attractive and are relatively easy to cultivate.

An easily cultivated species, it is primarily grown by cactus and succulent enthusiasts. The plants are terrestrial and require a large pot with a well drained cactus soil mix that is allowed to dry completely between waterings to bloom regularly in cultivation. In habitat the plants are found growing in spaces between rocks in sandy soils where the rock cracks they tend to grow in catch windblown organic materials. In cultivation, the plants must have achieved a sufficient root mass (5-6 pseudobulbs) to support the immense flower spikes which can reach 9 feet in height and carry 20-300 flowers in some cases. Blooming is triggered by withholding water from December through March and allowing the plants a dry resting period. Watering after this dormant period initiates flowering. Since this species is a desert adapted plant, like most desert species, flowering is triggered by availability of water after a dry dormant rest. A large, well flowered specimen of this species can be one of the most spectacular of orchids due to the size of the inflorescence and the large number of flowers produced.

The plants are robust and very attractive with large, yellow-green, fluted, sculptured pseudobulbs and stiff agave-like leaves which tend to not be deciduous as in most orchids. These plants tend to retain their leaves, much like an Agave for many years, even on older pseudobulbs. The leaves have stiff, serrated edges, much like an agave and resemble an agave leaf in texture. The plants are extreme xerophytes, and can go periods of up to a year without water provided the plants have a well established root system.

The plants can withstand intense heat and direct sunlight all day, but the plants pseudobulbs will darken and develop brownish pigmentation for UV protection and resemble plants found in habitat if subjected to direct sunlight and intense heat seasonally, and the plants look better if given some shade. Exposing the plants to temperatures below 40 degrees F for prolonged periods in wet soil will cause them to loose their roots and decline and the plants cannot tolerate freezing temperatures except for very short periods. The plants must be kept dry if they are subjected to below freezing temperatures. Although the plants are routinely subjected to below freezing temperatures in areas of their native range, they drop their leaves and bloom irregularly when subjected below freezing temperatures seasonally. Temperatures below 25 F for long periods will typically kill the plants.

Oddly, although this species is strictly terrestrial, its roots are large and covered in velamen similar to the roots of epiphytic orchids and like most orchids cannot tolerate sitting in standing water for long periods without loosing its roots. Unlike epiphytic orchids however, its roots are not deciduous and older roots do not die off as new pseudobulbs are produced, and the plants dislike being disturbed if flowers are desired. This species should be accommodated in a very large pot and only re-potted when the pot fills with pseudobulbs and the roots are completely constrained.

There are two distinct forms of this species encountered in the wild and in cultivation, and these forms often co-exist within a stand of wild plants. One form produces extremely thick short pseudobulbs and flowers with brown striping on the petals and very long flower spikes, sometimes 9 feet in height. The other form has slender pseudobulbs with longer more slender leaves and the plants are taller, and this variety produces very striking flowers with lime green petals, and somewhat shorter and more slender flower spikes. Both varieties have identical care and growing requirements.

While a few Eulophia species are self-fertile, this species does not appear to be and there are no reports of success in self-pollinating this species. In habitat the flowers along the immense inflorescence produced by this plant open slowly and in succession over a period of time and stands of these plants can be isolated over a considerable distance from one another. The large size of the inflorescence appears to have evolved to ensure flowers would be available over some period of time to pollinators since these plants are dependent on cross pollination, and insects may be required to travel some distance in order to transfer pollen from one plant to another. The majority of plants in habitat which do produce seed pods typically do so from flowers on the very top of the inflorescence from the last flowers that open sequentially. The plants also produce osmophores on the lower sections of the inflorescence which continue to emit chemical signals to attract pollinators as the infloresence develops, similar to Grammatophyllum and other orchid species which produce large inflorescences.

The seed pods of these plants are pear shaped and resemble a large yucca seed pod in shape and texture, although unlike a yucca, the seeds are dustlike and small, and the pod is approximately the size of a large pear.

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  Inflorescence with flowers

References

• Stewart, Joyce; Campbell, Bob (1970). Orchids of Tropical Africa. A.S. Barnes & Co. ISBN 0498075559. {{cite book}}: Invalid |ref=harv (help)