Blumea 57, 2013: 248–252 www.ingentaconnect.com/content/nhn/blumea RESEARCH ARTICLE http://dx.doi.org/10.3767/000651913X664009 Prophyll, calyculus, and perianth in Santalales J. Kuijt1 Key words Abstract The concepts of prophyll and calyculus in Santalales are reviewed, and are found to be of variable taxo- nomic importance in different families. The calyculus in Loranthaceae has been generally interpreted as a reduced biseriate corolla calyx, a concept recently challenged by Wanntorp & Ronse De Craene (2009), who concluded that it represents a calyculus fusion of prophylls. This view, as well as the accompanying biseriate corolla notion, is rejected. In Loranthaceae, prophyll prophylls associated with flowers have sometimes provided significant taxonomic features, while in Viscaceae this Santalales is true mostly in the vegetative portions of plants, especially in Arceuthobium, Dendrophthora and Phoradendron. Published on 1 February 2013 INTRODUCTION PROPHYLLS The Sandalwood order (Santalales) has been the subject of Even though the term ‘prophyll’ is often equated to ‘bracteole’, several significant studies in recent years. Most of these studies it has a more precise meaning, namely one of the two often have dealt with the phylogenetic history of the order and its mul- minute foliar organs that flank axillary axes in angiosperms, tiple components, especially the work of Nickrent et al. (2010). whether flowers, inflorescences, or vegetative ramifications. However, one of these contributions has instead focused on the The term ‘bracteole’ is used inconsistently in literature; they are structural elements related to flowers (Wanntorp & Ronse De usually associated with flowers, while prophylls do not share Craene 2009), and has resulted in some novel interpretations. that limitation. As will be seen below, prophylls are exceptionally It is the purpose of the present contribution to subject these important in Viscacean taxonomy, while bracteoles there are interpretations to scrutiny. non-existent. In Loranthaceae the obverse is true: prophylls as- The significant questions raised by Wanntorp & Ronse De sociated with flowers are extremely important in defining genera Craene (2009) revolve around three apparently distinct struc- in the New World, but those found at the base of vegetative axes tural issues. There is, first of all, the status and occurrence of are usually ignored. Only occasionally are they prominent in prophylls as defined below. Secondly, there is the erect rim of that position, as in some species of Psittacanthus (Kuijt 2009); tissue crowning the ovary of many but not all members of the the sharply pointed prophylls in the leaf axils of Tristerix appear order that is known as the calyculus. It has perhaps been the to be a generic feature (Kuijt 1988b, see f. 16e). Curiously, the most controversial morphological structure in the order, attract- verticillate branching pattern in Psittacanthus may occasionally ing various interpretations in the past. The third issue raised by indicate that prophylls do indeed exist there even though they Wanntorp & Ronse De Craene is whether the corolla represents may be scarcely recognizable; as mentioned for Arceuthobium a single or a double whorl of elements. As will be seen below, (Viscaceae) below, even scarcely recognizable prophylls may these three issues are linked by various interpretations. I begin subtend axillary ramifications. with a brief summary of the systematic occurrence of prophylls Being very inconspicuous, it is not surprising that prophylls have and the calyculus in Santalales. not been mentioned in descriptions of the majority of Santalalean In referring to families in Santalales, it is first necessary to deal taxa. It is entirely possible that prophylls do not exist in some with its recent reorganization as proposed by Nickrent et al. or all of a number of families. This applies, as far as I know, to (2010). These authors, largely on the basis of molecular data, Aptandraceae, Coulaceae, Eryrthropalaceae, Octoknemaceae, recognized 12 families, 4 of which are newly proposed. Crucial- Olacaceae, Schoepfiaceae, Strombosiaceae and Ximeniaceae. ly, the family Santalaceae is subdivided into 5 separate families. It is perhaps true for many Santalaceae as well, with exceptions A detailed critique of this reorganization falls outside the scope seen in many species of Thesium and especially in Thesidium, of the present article. However, since the family descriptions where each flower is flanked by a pair of large prophylls (Pilger are not adequately differentiated and contain important errors 1935, f. 40). The same author writes: “Meist sind zwei seitliche or undocumented statements, such as the supposed presence Vorblätter vorhanden”, but this is not borne out in the various of the calyculus in ‘Nanodeaceae’, I here prefer to maintain the generic descriptions. traditional concept of Santalaceae. The continued use of para- phyly in plant systematics has been substantially defended by Loranthaceae Brummitt (2006), Nordal & Stedje (2005), and especially Zander The loranthaceous material used in Wanntorp & Ronse De (2011). Since my taxonomic expertise is essentially limited to Craene’s (2009) study consists of one species each of Passovia the mistletoes and Santalaceae, I am using other family names (‘Phthirusa’) and Struthanthus. Each of these genera is char- from the Nickrent et al. (2010) treatment, but without prejudice. acterized by inflorescences bearing various numbers of paired, lateral triads. A triad consists of one central flower subtended 1 Department of Biology, University of Victoria, Victoria, BC V8W 3N5, by the primary bract (called pherophyll by Wanntorp & Ronse Canada; e-mail: [email protected]. © 2013 Nationaal Herbarium Nederland You are free to share - to copy, distribute and transmit the work, under the following conditions: Attribution: You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). Non-commercial: You may not use this work for commercial purposes. No derivative works: You may not alter, transform, or build upon this work. For any reuse or distribution, you must make clear to others the license terms of this work, which can be found at http://creativecommons.org/licenses/by-nc-nd/3.0/legalcode. Any of the above conditions can be waived if you get permission from the copyright holder. Nothing in this license impairs or restricts the author’s moral rights. J. Kuijt: Prophyll, calyculus and perianth in Santalales 249 De Craene) and a pair of flowers positioned in the axils of its Viscaceae prophylls. Triads may be pedunculate or essentially sessile on While in Loranthaceae prophylls appear to be of minor signifi­ the inflorescence axis. It should be added that the term ‘dicha- cance in the vegetative parts of plants, this is not so in several sium’ applied by Wanntorp & Ronse De Craene to lateral triads genera of Viscaceae. Nevertheless, here also they have not has also been variously circumscribed in botanical literature been given adequate attention. In Ginalloa and Notothixos (Lawrence 1951, Endress 2010). they have not been mentioned in the relevant literature, even The relevant new interpretation that the authors advance, though the inflorescences in the former genus appear to bear apparently based on SEM images, is that the prophylls of a them, as in the axillary ‘triads’ mentioned and illustrated in loranthaceous flower fuse to form its calyculus, as is also said Barlow (1997), where they subtend secondary lateral flowers. to be the case in Olacaceae. There is abundant evidence in the In Korthalsella we find an unclear situation in flower­bearing known structure especially of neotropical small-flowered Loran- regions (the concept ‘inflorescence’ itself is not always appli- thaceae to the effect that this interpretation (which here will be cable in the genus) but, again, there is no published record of called the ‘prophyllar hypothesis’) has flaws and is difficult to prophylls in vegetative parts of the plant (Barlow 1997). In fact, reconcile with the relevant literature, as detailed below. Mekel (1935) explicitly denies the presence of any prophylls in the axillary groups of flowers. The structure of triads and dyads When studying the triads of Struthanthus and Passovia as well Viscum as those of other Loranthaceae, it is immediately obvious that There appears to be no previous mention of prophylls in the their prophylls are physically far removed from the ovary of the extensive literature on Viscum. This is surprising in what is median flower. It follows that there cannot have been a devel- the most famous, and most written-about of all mistletoes, opmental connection between prophylls and calyculus. This V. album L. In V. album, there are regular, annual innovations is true not only for triadic small-flowered genera (all of which of one internode each, topped by one pair of foliage leaves and are neotropical), but also for Psittacanthus, Tripodanthus and a terminal inflorescence. At the very base of each innovation, others where the lateral flowers of triads (or, in Aetanthus and there is one pair of minute, translucent, fimbriate prophylls. some Psittacanthus species, dyads) are placed on elongated These structures are visible even during the winter, well before pedicels. In such cases, there is no evidence that the prophylls new innovations have started to elongate, and turn blackish in of the triad or dyad have a developmental relationship