Origin and Nature of Vessels in Monocotyledons. 7. Philydraceae and Haemodoraceae
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Journal oft/it Torrev Botanical Society 132(3). 25. pp. 377—383 Origin and nature of vessels in Monocotyledons. 7. Philydraceae and Haemodoraceae Edward L. Schneider”2 and Sherwin Cariquist Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, CA 93105 Canyon Road. Santa SCHNEIDER, E L. AND S. CARLQU,ST (Santa Barbara Botanic Garden. 1212 Mission J. Barbara, CA 93105. Origin and nature of vessels in monocotyledons. 7. Philydraceae and Haemodoraceae. scalariform Torrey Bot. Soc. 132: 377—383. 2005.—SEM studies of maccrated stems and roots showed that long In Haemodoraceae. perforation plates are present in roots and probably also stems of Philydrum (Philydraceae). In Clearly recognizable vessel elements are present in roots: perforation plates range from scalariform to simple. thread stems of Haemodoraceae, however, less clearly recognizable vessel elements are present: the presence of be like pit membrane remnants is one criterion that argues for vessel presence. Such tracheary elements can may considered transitional between tracheids and vessel elements. End walls of transitional tracheary elements than non have narrower bars between perforations, less prominent borders, and pit membrane remnants rather suggesting porose pit membranes. However, only one or two of these three character expressions may be present, show marked that clear definitions of vessel elements and tracheids may not be possible. Haemodoraceae a difference, or disjunction. in morphology between vessel elements rn roots and the vessel elements transhional may be to tracheids of stems. The physiological and evolutionary correlations of this morphological disjunction related to seasonality of water availability. Key words: Haemodoraceae. Philydraceae. tracheids. vessel elements, xylem evolution Philydraceae and Haemodoraceae have long monocotyledon families Acoraceae (Carlquist been considered closely related to each other, an and Schneider 1997) and Hanguanaceae idea confirmed in recent DNA-based phyloge (Schneider and Carlquist 2005). Such transition nies (Chase 2004, Davis et al. 2004). These two al tracheary elements are important in showing families are now considered 10 form, along with the phylogenetic origin of vessels in monocot Commelinaceae, Hanguanaceae, and Pontederi yledons. Study of xylem by means of scanning aceae. an order, Haemodorales (APG 11 2003 electron microscopy (SEM) clarifies the nature Chase 2004, Davis et al. 2004). The present of transitional tracheary elements, and thus il composition of this order, as noted by Chase luniinates the precise structural and ultrastruc (2004), results from molecular studies; in earlier tural nature of Ihis transition. Studies by means phylogenies, these families were placed in sev of light microscopy can show only part of the eral orders. Nomenclature follows MacFarlane nature of transitional tracheary elements, as is et al. (1987), Simpson (1998), and Goldblatt and evident from Cheadle’s (t968) notation of Manning (2000). “questionable perforations” in stem tracheary Philydraceae and Haemodoraceae are of spe elements of Anigozanthos r,’a Labill. cial interest with respect to xylem histology be Our sampling of Haemodoraceae and Phily cause Cheadle (1968) claimed that they had draceae is not as large as that of Cheadle (1968). clearly defined vessels in roots, but no vessels Cheadle studied the tracheary elements of 22 (or questionable ones in Anigozanthos of the Haemodoraceae and three Philydraceae. Simp Haemodoraceae) and thus only tracheids in son and Dickison (1981) studied the tracheary stems. Such a mode of occurrence of tracheary elements of Lachnanthes caroliniana and report elements offers the possibility of finding trache vessels with simple perforation plates in roots, my elements transitional between tracheids and vessels with scalariform perforation plates in of vessel elements (“vessel-tracheids” Palm rhizomes. and tracheids in leaves. We believe in the 1954). Such elements have been reported that the nature of tracheary elements in these Haemodoraceae and Philydraceae can be estab lished on the basis of the material we have ex communication: E-mail: eschneider@ Author for amined. Hopefully, our results offer a basis for sbbg.org tracheary el 2 The authors thank Virginia Hayes for material of further examination of transitional Wachendorfia thyrsifloro from the Lotusland Founda ements in a range of monocotyledons. The fam tion. We are grateful for textual assistance offered by ilies we have studied to date (Carlquist and and an anonymous reviewer. Michael G. Simpson Schneider 1997. 1998a, 1998b; Schneider and Received for publication November 15. 2004, and have been selected in revised form May 26. 2005. Carlquist 1997. 1998, 2005) 377 .3 ItS JOURNAL OF THE TORREY BOTANICAL SOCIETY [VOL. 132 because they represent Lineages in which Iran end wall facet shown (Fig. 3) appeals to us as a sitional tracheary elements seemed likely to oc probable perforation plate because of its wide cur. Families in which vessel elements are clear scataciform perforation plates. slender bars (of ly different from tracheids have not been includ ten forked), and absence of pit membranes. To ed in this series of papers. be sure, absence of pit membranes can occur because of handling of materials. Consequently, Materials and Methods. Roots and under in attempting to identify perforation plates in ground stems of living specimens of Philydrum stems, we sought features relating to pit mem lanuginosum Banks & Solander ex Gaertn., An brane remnants. In Fig. 4, a portion of a perfo igozanthos flavidus DC. ex Red., and Wachen ration plate shows threads and porose pit mem dorfia thyrsifiora Burin. were collected from brane fragments in what may be perfocations; plants under cultivation in Santa Barbara. Ma the presumptive lateral wall (Fig. 4. left) pos terials were fixed in 70% aqueous ethanol and sesses intact pit membranes. Pit membranes con then maccrated with Jeffrey’s Fluid (Johansen taining pores or holes of various sizes (Fig. 5) 1940). Macerations were spread onto aluminum were observed near the end of a presumptive stubs bearing electroconductive pads, dried in perforation plate. The delicate pit membranes il air, sputter coated with gold, and examined with lustrated in Fig. 5 are probably thinner than pit a Hitachi 52600>4 5PM using an accelerating membranes of typical lateral wall pits. and thus voltage of 25 kv. Care was taken to minimize can be interpreted as pits transitional to a per exposure of delicate pit membranes to the elec foration. tron beam, as such exposure at high power re Anigozanihos Ha vidus (Fig. 6—9). Vessel el sults in perceptible shrinkage and destruction of ements are identified pit membranes. easily in the root (Fig. 6— 8). Scalariform perforation plates may he seen Our criteria for recognizing perforation plates in narrower (likely early metaxylem) vessel el are as follows. Perforation plates are end walls ements. (Fig. 6—7). Scalariform perforation distinguishable from lateral walls by one or plates, whether longer (Fig. 6) or shorter (Fig. more of these features: absence of pit mem 7), appeared sunken (collapsed inward toward branes or presence of them as pit membrane the lumen) in our preparations, perhaps because remnants only; bars narrower between perfora the bars are so slender that they yield to the ten tions than corresponding secondary wall por sion involved in drying. The difference between tions of lateral wall pitting: and transitions be perforation plates and lateral wall pitting is read tween lateral wall pitting and perforation plates ily apparent in these elements (Fig. 6—7). Vessel visible as porose thin pit membranes: or pit bor elements with simple perforation plates (Fig. 8) ders narrower in perforation plates than on lat were somewhat more common eral wall pitting. than those with scalariform ones. Simple perforation plates are readily identifiable by their circular or oval out Results. Philydrurn laviuginosum (Fig. 1—5). lines, their smooth edges, and their obvious con Roots (Fig. 1—2) have scalariform perforation trast with lateral wall pitting (Fig. 8). plates with numerous bars in metaxylem vessel In stems, no clearly identifiable perforation elements (Fig. I). These were identified not only plates were observed on tracheary elements. On because of being on end walls of tracheary el end walls, a few adjacent pits were observed to ements, but also by virtue of having slender bars contain threadlike pit membranes (Fig. rather and no obvious pit membrane remnants in per 9) than laminar pit membranes. However, such pits forations.. A curious protoxylem tracheary ele are associated with thick intervening bars and rnent, representing a cell with transitions be have prominent borders (Fig. 9), features usually tween annular and helical thickenings and with associated with lateral wall pitting. conspicuous circuLar openings in primary wall areas, was observed (Fig. 2). We cannot present Wachendorfia thyrsifiora (Fig. /0—13). In this with certainly as a vessel element, if only the roots of W. thyrsiflora. perforation plates ap because so few protoxylem vessel elements have peared to be simple (Fig. 10—Il). However, been identified and illustrated in monocotyle close examination of some perforation plates re dons, and thus available comparisons are few. vealed probable bars at the end of the perfora In stems of P. lanugnurcum, a few tracheary tion plate near (he cell tip (Fig. 10). and thus element facets referable to the concept of per one might designate a few plates as scalariform. foretlon plates were observed (Pig, 3—5). The although not in the ordinary sense. Vessel dc. 2005] SCXNEIDER AND CARI.QUIST ORIGIN OF VESSELS IN MONOCOTYLEDONS 379 I ii I I :3. I - so, 1’ a 1 aa e -L a 5 Fir,. 1—5, SEM photographs of tracheary elements in roots (Fig. 1—2) and stems (Fig. 3—5) of Philydrum lwlugtnUsum. Fig. I. Perforation plate of a melaxylem vessel. Fig. 2. Possible perforation plate of a proioxylem tracheary element. Fig. 3. Apparent perforation plate in a metaxylem element. Fig. 4. Portion of a facet of a element: threads and pit membrane portions suggesting the presence of perforations. Fig. 5.