Aloe tomentosa is unusual within the huge diversity of this large genus, since it is one of a small group with hairy flowers that have a limited distribution in the Horn of Africa and southern Arabia

Walker, Colin

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Open Research OnlineThe Open University’s repository of research publicationsand other research outputsAloe tomentosa - a species with unusual hairy flowersfrom the YemenJournal ItemHow to cite:Walker, Colin (2016). Aloe tomentosa - a species with unusual hairy flowers from the Yemen. CactusWorld,34(3) pp. 153–158.For guidance on citations see FAQs.c© 2016 BCSS, authors and illustrators of individual articlesVersion: Version of RecordCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.uk153CactusWorld 2016 Vol. 34 (3)Aloe is a large genus of over 500 species (Carter etal, 2011) and even today that number continuesto increase.  Of these, a very small number of species,perhaps no more than 20, are unusual in having hairyflowers.  These are concentrated in southern Arabiaand the Horn of Africa.  In respect of Saudi Arabia, forexample, Collenette (1999) records 22 species of Aloeand two hybrids. Three of the Saudi aloes have hairyflowers, which represents only 12.5% of the totalnumber of aloes recorded forthis large country.  In Oman, Miller et al (1988) record noaloes with hairy flowers.Further south in mainlandAfrica, Sebsebe Demissew &Nordal (2010) accept six speciesout of 46 with hairy flowers forEthiopia and Eritrea, making13% of that total.  For the smalladjacent country of Djibouti,Ruch et al (2013) recognise thatnearly half the species, ie fourout of a total of nine (44%), arehairy-flowered species.  Furthereast in Somalia, Lavranos (1995)similarly identifies four specieswith hairy flowers, but thisrepresents only 12.9% of thetotal of 31 recognised species inthis larger country.  The mostrecently described hairy-flowered Somali species is Aloeanodonta T.A.McCoy &Lavranos (McCoy & Lavranos,2015).  The furthest south thathairy-flowered aloes have beenrecorded on the African continent is northern Kenya:Aloe citrina S. Carter & Brandham (Carter et al, 2011).Madagascar, with its great diversity of aloes, currentlytotalling perhaps 150 taxa, has no hairy-floweredspecies at all (Castillon & Castillon, 2010).  The names of a few of these species indicate thehairiness of the flowers, ranging from shortly downy toconspicuously very hairy.  Aloe pubescens Reynoldswas named for its pubescent or finely hairy flowers,Aloe tomentosa – a species with unusual hairy flowers from the YemenColin C WalkerAloe tomentosa is unusual within the huge diversity of this large genus, since it is one of a smallgroup with hairy flowers that have a limited distribution in the Horn of Africa and southern Arabia.Photography by the author.Fig. 1  Seedlings of Aloe tomentosa at about two years old154 CactusWorld 2016 Vol. 34 (3)Aloe trichosantha A.Berger for the hairy perianth, Aloelanata T.A.McCoy & Lavranos for the woolly flowers,and the principal subject of this current article, Aloetomentosa Deflers, which is tomentose with flowerscovered in densely matted hairs.  One term that has yetto appear as a specific name in Aloe for a hairy-flowered species is hirsute, ie as Aloe ‘hirsuta’.Of these hairy-flowered species, A. tomentosa was thefirst to be discovered and described from the Yemen,thus it would seem appropriate to begin with asummary of its history. Botanical exploration ofArabia began with Pehr Forsskål (1732–1763), whowas a member of the Royal Danish expedition toArabia Felix, modern day Yemen.  The expedition wasabroad from 1761 to 1763 and travelled via Egypt onroute to the Yemen.  It was ill-fated since all but one ofthe participants died on route, with Forsskål himselfsuccumbing to plague in July 1763 (Hepper & Friis,1994).  Fortunately Forsskål’s work was not in vain,since his work resulted in the first flora of Arabia(Forsskål, 1775), which was published posthumouslyby an editor, Carsten Niebuhr, who was an astronomerand mathematician, but not a botanist.  Forsskål’s floraincludes seven aloes, of which four are currentlyrecognised (Walker, 2005), but none of which havehairy flowers.The French botanist, Albert Deflers (1841–1921),followed in Forsskål’s footsteps in the ArabianPeninsula over 120 years later, and it was he whodiscovered and named the first hairy-flowered Aloe.  In1887, having obtained permission from the Ministry ofPublic Education, Deflers carried out a botanical studyFig. 2  Aloe tomentosa, mature plants in 25cm pots155CactusWorld 2016 Vol. 34 (3)in Arabia.  Whereas Forsskål was obliged to confine hisobservations to the Tihama – the lower slopes of themountains – between Lohaja, Hodeida and Taiz,Deflers explored the highlands of Yemen to an altitudeof around 2,800m above sea level.  He travelled toHodeida on the Red Sea, then went to Sana’a andexplored the mountainous region, travellingsouthwards via Yerrim and Sedda, as far as Aden(Walker, 1999).  The story of this journey waspublished as a book in 1889 with the title Voyage auYemen (Journey to the Yemen) (Deflers, 1889). Compared to Forsskål, Deflers visited previouslyunexplored areas of Arabia and this, no doubt,accounts for his new botanical discoveries.  He was notespecially interested in succulents in general or in Aloein particular.  However, it is worth noting that later(Deflers, 1896) he published a separate study ofArabian asclepiads (formerly members of theAsclepiadaceae, now in the combined familyApocynaceae) of which he included 47 species.  Ofthese, 24 are succulent and eight newly described,notably stapeliads and ceropegias (Walker, 1999).For Aloe in the Yemen, Deflers (1889) recorded anddescribed just three species: Aloe officinalis Forsskål(altitude 200m); an Aloe species for which he gave noname (altitude 1,000–1,200m), and most significantly,Aloe tomentosa Deflers.  His new species was recordedfrom Jabal Hadhur, near the village of Bauân, at2,700m.  Note this high altitude, not reached earlier byForsskål.  Most importantly, this new species isdescribed in reasonable detail, and interestingly with aperianth that was densely lanate, ie woolly.  So this isthe first description of a hairy-flowered Aloe.Next on the scene was Gilbert Reynolds, doyen of Aloestudents from 1930 to 1966 (Walker, 2010).Regrettably for his work on tropical aloes (Reynolds,1966), he was never able to visit Arabia.  He did,however, visit Somalia, where he found a species withhairy flowers growing in considerable numbers nearMoledera, south of Erigavo.  He wrote (Reynolds,1958) that “allowing for geographical variations, andfor racemes varying from shorter and denser to longerand laxer, I now regard the Moledera plants asbelonging to A. tomentosa.  Compared with the type,the Moledera form differs in having slightly longer,less dense racemes, with the apical buds less crowdedand less hidden by their bracts . . . [So] I conclude thatthe Moledera plants are conspecific withA. tomentosa.”  In his monumental monograph of thealoes of tropical Africa and Madagascar, he took thesame stance: A. tomentosa occurred both in the Yemen(its type locality) and in Somalia (Reynolds, 1966).Somewhat later, Lavranos & Glen (1989) reassessedthe plants at Moledera, Somalia and described these asa new species, Aloe molederana Lavranos & Glen.They concluded that “Aloe molederana appears to beonly very remotely related to the true A. tomentosa”,differing “in its clumped habit, smaller leaves, few-branched inflorescences, lax to subdense racemes andpink flowers”.  Their dendrogram, which illustratessimilarities between species based on morphologicalfeatures, has A. molederana far removed fromA. tomentosa.  The Moledera species, which has a veryFig. 3  Aloe tomentosa in flower at about 10 years old from seed156 CactusWorld 2016 Vol. 34 (3)restricted distribution, is also geographically farremoved from where Deflers first collectedA. tomentosa in Yemen.  Consequently, the separationof A. molederana from A. tomentosa is justified onmany counts, and this reinstates the latter species as aYemeni endemic.Following Reynolds on the Aloe scene in Arabia wasJohn Lavranos, well known for his discoveries inArabia and further afield.  He collected a hairy-flowered species that was named Aloe lavranosiiReynolds in his honour (Reynolds, 1964), of whichmore later.  Its type locality was at that time part of theWestern Aden Protectorate, not then part of theYemen.  Lavranos (1965) in his studies of the aloes ofArabia had at that time, like Reynolds before him, notbeen able to revisit Deflers’s type locality forA. tomentosa. Returning to the Yemen proper, where the trueA. tomentosa had been studied by Wood (1983, 1997)over a 10-year period, and nearly 100 years after thediscovery by Deflers, Wood recognised 17 species,which he divided into seven groups.  Hislargest group consists of six species withmostly solitary stemless plants withhairy flowers: Aloe doei Lavranos,A. menachensis (Schweinfurth) Blatter,A. niebuhriana Lavranos, A. tomentosaand two unnamed species. Wood considered A. tomentosa to be “avery distinct species with massive leafrosettes and a densely hirsuteinflorescence of greenish-white flowers”and it “is set apart from other membersof this group by the high altitudes itgrows at and by its summer floweringseason (April to September)”.Incidentally, Wood (1983) was also thefirst to question the inclusion of theSomali plants from Moledera inA. tomentosa, the position later resolvedby Lavranos & Glen (1989), as outlinedearlier.In terms of the distribution ofA. tomentosa in Yemen, Wood (1997)records this species as being “frequenton rocky hillsides between 2,400 and3,100m on the mountains surroundingthe high plateau.  It is absent from theouter escarpment apart from isolatedrecords.”It would now be appropriate to consider A. tomentosain cultivation.  I have been growing it for nearly tenyears having obtained seed in 2006 which wasgerminated successfully by Tina Wardhaugh, andthree seedlings have grown well since then (Fig. 1).Like many aloes, the seedlings had initiallydistichously-arranged leaves, either well-spotted(maculate) or hardly spotted at all (immaculate).  Isuspect that leaf spotting in the juvenile state hassomething to do with protection, providingcamouflage, but there is no evidence as yet to supportthis hypothesis.  My plants have continued to growwell and were repotted into 25cm-diameter pots in2014 (Fig. 2).  The plants at maturity are stemless andsolitary.  The leaves are virtually spotless at maturity,and dull glaucous grey-green in colour, up to 35cmlong and 9cm at their widest, with the marginsadorned with sharp, short brown teeth 1mm long andup to 2cm apart.One of the three plants produced the first inflorescencein August 2015 (Fig. 3) and it is interesting to note thatFig. 4  Closer view of the inflorescence157CactusWorld 2016 Vol. 34 (3)this is the only one that has flowered so far.  Theinflorescence is 72cm tall with five branches, up to23cm long.  Each raceme is up to 12cm long, denselyarranged with flowers and conical in shape (Fig. 4).The perianth is 25–27mm long and its tepals are whitewith a central green stripe (Fig. 5).  This flower colouris in itself interesting, since the vast majority of aloeshave flowers in the spectrum yellow, through orange todeep red or even scarlet.  White and green to greenish-white coloured flowers are unusual.  The flowersproduce copious amounts of yellow nectar that dripsonto the plant leaving a sticky deposit that needs to beremoved. The principal unusual feature of these flowers is, ofcourse, that they are hairy (Figs. 5 & 6).  Deflers (1889)described the perianth as lanate, but described hisnovel new species as tomentosa rather than lanata.  Iwould describe these flowers more as lanate, meaningwoolly, rather than tomentose.  The hairs are up toabout 1.5–2.0mm in length and are intertwined, butsoft like wool and not at all stiff and bristle-like (Fig. 6).Technically these are trichomes, and each perhapsconsists of a single or just two cells.  The upper part ofthe inflorescence branches are also hairy, but perhapsbetter described as being pubescent or puberulent,with a covering of very much shorter trichomes.  Thelower part of the peduncle is smooth and hairless.The immediate question is: what is the function of thehairs on the flowers of aloes such as A. tomentosa?The obvious hypothesis is that their presence playssome active role in pollination, possibly in attractingbird pollinators, as sunbirds are pollinators in manyAfrican countries.  Yemen hosts four species ofsunbird, according to an internet search carried out byTom Eichler and posted to the BCSS Forum (Walker etal, 2015).  As far as I am aware, there are no publishedobservations of birds pollinating aloes in Arabia, so fornow the relationship between greenish-white colouredflowers, their hairy perianths and potential pollinatorsis merely speculation.  Field observations of theseplants in flower in the wild are required to resolvethese interesting questions.Finally, what is the relationship of A. tomentosa toother hairy-flowered species?  Aloe lavranosii (whichincludes Aloe splendens Lavranos and A. doei; McCoy& Lavranos, 2010) mentioned earlier, is an obviouschoice as a near relative, but differs in having a muchmore laxly (loosely) arranged raceme with a red oryellow perianth, which ranges from glabrous (so nothairy at all) through to sparsely pubescent, but not sodensely lanate as in A. tomentosa.  Another specieswith densely lanate flowers is A. lanata, another higheraltitude Yemeni endemic with a red perianth,described since the last survey of Yemeni aloes byWood (1997).In terms of evolutionary relationships, the mostextensive cladogram (evolutionary tree) produced todate is that of Grace et al (2015).  In this, A. tomentosahas been shown to sit in a clade (tree branch) alongwith other aloes of the Arabian Peninsula, includingother hairy-flowered species such as A. splendens (=A. lavranosii) and A. niebuhriana.  However, the cladeFig. 5  Aloe tomentosa flowers showing the hairy surface to theperianth158 CactusWorld 2016 Vol. 34 (3)also includes several glabrous (hairless) floweredspecies such as Aloe inermis Forsskål and A. pendensForsskål.  Other non-Arabian species with tomentoseflowers, such as A. trichosantha from Eritrea, are farremoved in the cladogram, so it is possible that hairyflowers evolved more than once as Aloe speciationradiated northward from the origin of the genus insouthern Africa into the Horn of Africa and Arabia(Grace et al, 2015).ACKNOWLEDGEMENTS:I am indebted to Tina Wardhaugh for raising my three specimensfrom seed.  I would also like to thank members of the BCSS Forum,especially Tom Eichler, for discussion of this and related species.Thanks also go to my wife Marjorie for comments on an early draftof the manuscript.LITERATURE CITED:Carter, S, Lavranos, J J, Newton, L E & Walker, C C (2011) Aloes.The Definitive Guide.  Kew Publishing, Royal Botanic Gardens,Kew / British Cactus & Succulent Society. Castillon, J-B & Castillon, J-P (2010) Les Aloe de Madagascar / TheAloe of Madagascar.  Privately published, Etang-Salé, Île de laRéunion.Collenette, S (1999) Wildflowers of Saudi Arabia.  NationalCommission for Wildlife Conservation and Development,Kingdom of Saudi Arabia. Deflers, A (1889) Voyage au Yemen. Journal d’une excursionbotanique faite en 1887 dans les montagnes de l’Arabie Heureuse.Paul Klincksieck, Paris.- (1896) Les Asclépiadeés de l’Arabie Tropicale.  Mem. Inst. Egypt 3:253–283, tt.1–6.Forsskål, P (1775) Flora Aegyptiaco-Arabica.  Moller, Copenhagen.Grace, O M, Buerki, S, Symonds, M R E, Forest, F, van Wyk, A E,Smith, G F, Klopper, R R, Bjorå, C S, Neale, S, Demissew, S,Simmonds, M S J & Rønsted, N (2015) Evolutionary history andleaf succulence as explanations for medicinal use in aloes andthe global popularity of Aloe vera.  BMC Evolutionary Biology15:29: 1–12.Hepper, F N & Friis, I (1994) The plants of Pehr Forsskål’s FloraAegyptiaco-Arabica. Royal Botanic Gardens, Kew / BotanicalMuseum, Copenhagen.Lavranos, J J (1965) Notes on the aloes of Arabia with descriptionsof six new species. J. S. Afr. Bot. 31: 55–81.- (1995) Aloaceae in Thulin, M (ed.) Flora of Somalia, Vol. 4, pp.35–42. Royal Botanic Gardens, Kew.Lavranos, J J & Glen, H F (1989) Aloe molederana. Flow. Pl. Afr. 50:t.1982.McCoy, T A & Lavranos, J J (2010) Nomenclatural notes on certainArabian aloes. CactusWorld, 28(1): 29–30.- (2015) Two new additions to the genus Aloe from Somalia.CactusWorld 33(3): 179–184.Miller, A G, Morris, M & Stuart-Smith, S (1988) Plants of Dhofar.The southern region of Oman. Traditional, economic and medic-inal uses. The Office of the Advisor for Conservation of theEnvironment, Diwan of Royal Court, Sultanate of Oman.Reynolds, G W (1958) The identity of Aloe somaliensis Watson(Somaliland Protectorate), and of A. tomentosa Deflers(Arabia).  J. S. Afr. Bot. 24: 163–168, pls. XI–XV.- (1964) A new Aloe from S.-W. Arabia. J. S. Afr. Bot. 30: 225–227,pls. XXXI–XXXII.- (1966) The aloes of tropical Africa and Madagascar.  The AloesBook Fund, Mbabane, Swaziland.Ruch, N, McCoy, T & Grace, O M (2013) The genus Aloe L.(Xanthorrhoeaceae) in Djibouti.  Bradleya 31: 15–24.Sebsebe Demissew & Nordal, I (2010) Aloes and lilies of Ethiopia andEritrea.  Shama Books, Addis Ababa, Ethiopia.Walker, C C (1999) Arabian asclepiads of Albert Deflers.  Asklepios76: 23–32.- (2005) A tale of two Arabian aloes.  Brit. Cact. Succ. J. 23(4):175–179. - (2010) Gilbert Westacott Reynolds: his study of Aloe and a bibli-ography of his work.  Bradleya 28: 111–124.Walker, C C et al (2015) Aloe tomentosa – a hairy-flowered aloe.BCSS Forum. www.bcss.org.uk/foruma/viewtopic.php ?f=1&t=163769Wood, J R I (1983) The aloes of the Yemen Arabia Republic. KewBull. 38: 13–31, pls. 1 & 2.- (1997) A handbook of the Yemen flora.  Royal Botanic Gardens,Kew.Colin C WalkerDept of Environment, Earth & Ecosystems,The Open University, Milton Keynes, MK7 6AAEmail: Colin.Walker@open.ac.ukLayout by Stephen MorrisFig. 6  Bud of Aloe tomentosa with the dense covering of hairs(trichomes)

Aloe tomentosa - a species with unusual hairy flowers from the Yemen

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Aloe tomentosa - a species with unusual hairy flowers from the Yemen

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