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A mature tree of Phytolacca dioica growing on the grounds of the School of Gardening and Landscaping in Petah Tiqwa, Israel. FIG. 2. Cross section of a young medullary bundle consisting of two vascular strands immediately above the level at which it departs from the vascular cylinder. The arrows indicate the protoxylem poles of the developing strands, X425. FIG. 3. Cross section showing the departure of two vascular strands from the vascular cylinder. x 128. FIG. 4. Cross section of a medullary bundle just below the insertion of the leaf to whieh this bundle departs. The arrow shows the direction in which the leaf base lies. x89. FIG. 5. Cross section of a medullary bundle after the beginning of cambial activity. The arrows indicate the primary xylem poles. x96. Fla. 6. Cross section of a medullary bundle with secondary growth just above its departure from the vascular cylinder. The arrow indicates the area of cambial discontinuity. C, eambium, X93.
Source publication
P. dioica has a primary vascular system which includes medullary bundles. The primary structure of these bundles is composite, consisting of 2-4 collateral vascular strands with their phloem poles oriented toward a common center. A cambium is formed between the xylem and phloem of the strands and extends to enclose the phloem of the whole bundle. A...
Context in source publication
Context 1
... vascular strands which enter the pith and form new medullary bundles may do so either on the cathodic or the anodic side of the medullary bundle departing to the leaf. The side of the leaf on which the new medullary bundle arises is related to the phyllotactic fraction of the stem but not to the direction of the ontogenetic helix. Shoots with 2/5 or 2/7 phyllotaxy always give rise to the new medullary bundles on the cathodic side of the leaf trace, while in shoots with 3/8 phyllotaxy they arise on the anodic side. This relationship is identical to that found for the direction in which the median leaf traces branch form sympodial bundles. When the phyllotactic fraction is 1/3, 3/8, 8/21, or 3/11 , the branching is anodic; when the fraction is 2/5, 5/13, 2/7, or 5/18, it is cathodic (Namboodiri and Beck 1968). These relationships can be understood by considering the relationship between the arrangement of leaves at the apex and the vascular pattern. Figure 11 is a cross section of an apex with a divergence angle of approximately 137.5°. The leaves are numbered along the ontogenetic helix from older to younger. A line drawn from the center of the apex through the center of an older leaf (leaf 0) passes closer to the centers of leaves 3, 5, 8, 13, 21, etc. (i.e., leaves numbered in the Fibonacci series), then to the centers of any other leaves. The centers of the higher numbered leaves are closer to the line than are those of the lower numbered leaves. It can also be seen that leaves numbered alternately in the Fibonacci series lie on alternate sides of the line. The mathematical basis of these facts has been explained by Richards (1951), Mitchison (1977), and Jean (1984). Now, if the phyllotactic fraction characterizing this apex is p/n, then every nth leaf will be linked to the same sympodium. However, since there are no leaves that arise directly above one another, the leaves will be linked either in the cathodic (left side of the line in Fig. 11) or anodic (right side of the line in Fig. I I) direction from the previous leaf. When n 3, 8, 21, etc., the trace linkage is anodic; when n = 5, 13, etc., it is cathodic. Similar arguments can be made for apices which have divergence angles other than 137.5°. All of the divergence angles found in plants with helical phyllotaxy (Dormer 1972) show the same properties as this angle. The direction of the median trace linkage is, thus, determined by the divergence angle and the denominator of the phyllotactic fraction and is independent of the direction (sinistrorse or dextrorse) of the phyllotactic helix. As is well known, the denominator is also the number of sympodia in a stem and is related to leaf arrangement at apex in a precise way (Kirchoff ...
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Citations
... In contrast, medullary bundles are ubiquitous throughout the Nyctaginaceae, absent only in the tribe Leucastereae (Cunha Neto et al., 2020a), and are present also in closely related families of the phytolaccoid clade (e.g. Phytolaccaceae: Kirchoff & Fahn, 1984). Within this clade, the acquisition of medullary bundles (but not the evolution of the climbing habit) is associated with increased diversification rates (Cunha Neto et al., 2022). ...
... Our findings demonstrate that typical medullary bundles are not the only type of conducting vascular tissues in the pith (CVTP) in Caryophyllales. Considering their developmental origin, medullary bundles (CVTP -TYPE 1) have been classified into two main categories (De Bary, 1884;Wilson, 1924;Kirchoff & Bundles tend to assume this form after secondary growth (Kirchoff & Fahn, 1984). 4 Bundles tend to assume this form after continued secondary growth (Maheshwari & Singh, 1942 ...
... Our findings demonstrate that typical medullary bundles are not the only type of conducting vascular tissues in the pith (CVTP) in Caryophyllales. Considering their developmental origin, medullary bundles (CVTP -TYPE 1) have been classified into two main categories (De Bary, 1884;Wilson, 1924;Kirchoff & Bundles tend to assume this form after secondary growth (Kirchoff & Fahn, 1984). 4 Bundles tend to assume this form after continued secondary growth (Maheshwari & Singh, 1942 ...
The occurrence of conducting vascular tissue in the pith (CVTP) of tracheophytes is noteworthy. Medullary bundles, one of the remarkable examples of CVTP, evolved multiple times across angiosperms, notably in the Caryophyllales. Yet, information on the occurrence of medullary bundles is fragmented, hampering our understanding of their structure–function relationships, and evolutionary implications.
Using three plastid molecular markers (matK, rbcL, and rps16 intron), a phylogeny is constructed for 561 species of Caryophyllales, and anatomical data are assembled for 856 species across 40 families to investigate the diversity of medullary bundles, their function, evolution, and diversification dynamics. Additionally, correlated evolution between medullary bundles and successive cambia was tested.
Medullary bundles are ancestrally absent in Caryophyllales and evolved in core and noncore families. They are structurally diverse (e.g. number, arrangement, and types of bundles) and functionally active throughout the plant's lifespan, providing increased hydraulic conductivity, especially in herbaceous plants. Acquisition of medullary bundles does not explain diversification rate heterogeneity but is correlated to a higher diversification rate.
Disparate developmental pathways were found leading to rampant convergent evolution of CVTP in Caryophyllales. These findings indicate the diversification of medullary bundles and vascular tissues as another central theme for functional and comparative molecular studies in Caryophyllales.
... In addition, D. paniculata differs from Machaerium multifoliolatum and other Fabaceae species given that the formation of new cambia does not cause severe changes in stem conformation. On the other hand, the occurrence of successive cambia in tree species is observed also in different groups, including Acanthaceae (Robert et al., 2011;Schmitz et al., 2008), Convolvulaceae (Terrazas et al., 2011;personal observation) and Phytolaccaceae (Kirchoff and Fahn, 1984;Rajput et al., 2012b;personal observation). ...
... Increase in stem thickness and the mechanism of cambial action in Amaranthaceae, Chenopodiaceae and Phytolaccaceae has attracted the attention of several researchers since long (De Bary, 1884;Solereder, 1899;Artschwager, 1926;Pfeiffer, 1926;Balfour, 1965;Philipson and Ward, 1965;Costea and DeMason, 2001). Due to the unique mechanism of their secondary growth in such plants is referred as "abnormal secondary growth" in the earlier literature (De Bary, 1884;Solereder, 1899;Artschwager, 1926;Pfeiffer, 1926;Studholm and Philipson, 1966;Balfour, 1965;Philipson and Ward, 1965;Fahn and Shchori, 1967;Philipson et al., 1971;Stevenson and Popham, 1973;Mikesell, 1979;Horak, 1981;Kirchoff and Fahn, 1984;Costea and DeMason, 2001). However, use of the term "cambial variant" is recommended by Carlquist (1988Carlquist ( , 2001Carlquist ( , 2004Carlquist ( , 2007a because the word 'abnormal' gives misleading sense. ...
... It is also well documented that plants in which stem thickness increase by forming successive cambia; the first successive cambium always forms after the formation of few derivative of the secondary xylem (Balfour, 1965;Philipson and Ward, 1965;Rajput, 2002;. However, present study revealed diverse results than the previously reported cases in Amaranthaceae, Chenopodiaceae and Phytolaccaceae (Studholm and Philipson, 1966;Balfour, 1965;Philipson and Ward, 1965;Fahn and Shchori, 1967;Philipson et al., 1971;Stevenson and Popham, 1973;Mikesell, 1979;Horak, 1981;Kirchoff and Fahn, 1984;Costea and DeMason, 2001;Rajput, 2002). As evidenced in Fig. 1D-F, in both species of Suaeda, vascular bundles failed to establish complete cylinder of the regular vascular cambium; therefore, first complete ring of the cambium (successive cambium) initiated from the parenchymatous cells external to the protophloem. ...
Amaranthaceae s.l. and its allied families like Amaranthaceae s.s., Chenopodiaceae s.s. and Phytolaccaceae s.s. are always debated in the literature about their pattern of secondary growth; when their stem diameter increases by forming successive cambia. In the present study, development of successive cambia and differentiation of its derivatives was investigated in Suaeda fruticosa and S. nudiflora (Amaranthaceae s.l.). After primary growth, the first complete ring of cambium was formed by the successive cambium due to failure in the development of interfascicular cambium between adjacent vascular bundles. The first ring of successive cambium initiated from the parenchymatous cells (pericyclic derivatives)external to the protophloem. This newly formed cambium was functionally bidirectional and produced secondary xylem centripetally and phloem centrifugally. Subsequent renewal of cambium was observed as small segments instead of complete ring. They interconnect with existing cambium and form anastomosing network. Due to the renewal of small sectors, the secondary phloem formed by earlier cambial segments became enclosed within the secondary xylem and conjunctive tissue. Formation of vessels and sieve elements were found confined only to few fusiform cells while rest of the cambial sector exclusively produced conjunctive tissue on either side. The secondary xylem formed in the beginning of successive rings of xylem remained rayless while thick stems showed presence of heterocellular rays with several cells in height and width. Accumulation of starch along with the presence of nuclei in the xylem fibres even after deposition of the secondary wall is consistent feature in both the species.
... INTRODUCTION The structure of the primary and secondary vascular systems of Phytolacca dioica (L.) differs from that of most dicotyledons. The primary vascular system contains medullary bundles and has recently been investigated by Kirchoff and Fahn (1984). The secondary vascular system is characterized by anomalous secondary thickening taking place by means of supernumerary cambia (Solereder 1908;Metcalfe and Chalk 1950). ...
... The primary vascular system of Phytolacca dioica has previously been described in detail (Kirchoff and Fahn 1984). Here, we will briefly summarize only those features of the primary body which relate to the present research. ...
P. dioica (L.) is characterized by anomalous secondary thickening by means of supernumerary cambia. After a period of primary growth and the formation of an initial (normal) vascular cambium, supernumerary cambia are initiated outside of the primary vascular cylinder. The initiation of the 1st supernumerary cambium takes place through approximately the number of nodes equal to the denominator of the phyllotactic fraction characterizing a given axis. At each node a semgent of supernumerary cambium is initiated opposite the left traces suppyling the leaf inserted at that node. The segments of differentiated cambium are preceded by regions of obliquely and anticlinically dividing cells. In the single juvenile axis studied supernumerary cambial segments also appear above the node to the cathodic side of the entering leaf traces, and opposite the medullary bundle immediately anodic to these traces. Vascular connections among the primary and supernumerary vascular cylinders occur between leaf insertions on the same orthostichy. The levels at which these connections occur vary among stems. The switch from ordinary to anomalous secondary growth may be caused by a change in tissue response to stimuli produced by leaves.
Premise:
Medullary bundles, i.e., vascular units in the pith, have evolved multiple times in vascular plants. However, no study has ever explored their anatomical diversity and evolution within a phylogenetic framework. Here, we investigated the development of the primary vascular system within Nyctaginaceae showing how medullary bundles diversified within the family.
Methods:
Development of 62 species from 25 of the 31 genera of Nyctaginaceae in stem samples was thoroughly studied with light microscopy and micro-computed tomography. Ancestral states were reconstructed using a maximum likelihood approach.
Results:
Two subtypes of eusteles were found, the regular eustele, lacking medullary bundles, observed exclusively in representatives of Leucastereae, and the polycyclic eustele, containing medullary bundles, found in all the remaining taxa. Medullary bundles had the same origin and development, but the organization was variable and independent of phyllotaxy. Within the polycyclic eustele, medullary bundles developed first, followed by the formation of a continuous concentric procambium, which forms a ring of vascular bundles enclosing the initially formed medullary bundles. The regular eustele emerged as a synapomorphy of Leucastereae, while the medullary bundles were shown to be a symplesiomorphy for Nyctaginaceae.
Conclusions:
Medullary bundles in Nyctaginaceae developed by a single shared pathway, that involved the departure of vascular traces from lateral organs toward the pith. These medullary bundles were encircled by a continuous concentric procambium that also constituted the polycyclic eustele, which was likely a symplesiomorphy for Nyctaginaceae with one single reversion to the regular eustele.
A relatively large number of dicotyledonous plants exhibit anomalous secondary thickening. In all or many species of about 55 families phloem strands become included in the secondary xylem as a result of anomalous growth.
Vascular anatomy of the Caryophyllales provides an interesting database that has potential for phylogenetic analyses, given that several peculiar apomorphic features have been documented within the order. Chief among the structural oddities is anomalous secondary growth of roots and stems, wherein most secondary thickening of vascular tissues is produced by arcs of lateral meristems that are formed to the outside of the initial vascular cambium of the organ (Pfeiffer 1926; Esau 1965a). Even during the last century anatomists recognized that anomalous secondary thickening characterizes several closely related centrospermous families (Sanio 1863; de Bary 1884; Georghieff 1887; Solereder 1908), and this feature has been used for evaluating familial relationships (Eckardt 1976; Cronquist 1981; Thorne 1983; Gibson and Nobel 1986). Nonetheless, reporting on anomalous secondary thickening in stems and roots of different ages has been incomplete. Primary shoot vasculature of this order also includes some fascinating variations, e.g., the apparent occurrence of vascular bundles within pith (Wilson 1924; Dastur 1925; Joshi 1934; Metcalfe and Chalk 1950; Pant and Mehra 1961) and open and closed systems within the same family (Wilson 1924; Bisalputra 1962; Gibson 1976; Beck et al. 1982).
Herbs, shrubs, more or less woody climbers, or trees. Leaves alternate (opposite in Gisekia), simple, entire, usually petiolate; stipules absent (but sometimes prophylls of axillary bud resembling stipules; transformed into spines in Seguieria). Inflorescences mostly indeterminate (determinate in Seguieria and Agdestis), most frequently racemes or spikes. Flowers small, bisexual (unisexual in Monococcus and a few species of Phytolacca and Ledenbergia, plants usually dioecious), mostly actinomorphic (± weakly zygomorphic in Hilleria and Anisomeria), hypogynous (nearly epigynous in Agdestis). Perianth simple, tepals 4 or 5, free (slightly connate in Hilleria), imbricate, inconspicuous to petaloid, mostly greenish to whitish, less often yellow or reddish. Stamens (2−)4 to many, free; anthers dorsifixed, tetrasporangiate, mostly more or less linear (subglobose in Microtea), at the base incised, often also at the tip, opening by longitudinal slits. Carpels 1–17, arranged in one whorl (inserted on a gynophore in Nowickea), free or more or less united; styles usually free or absent (united in Agdestis); stigmas free. Ovules one per carpel (in Microtea and Lophiocarpus one per ovary), campylotropous, bitegmic, crassinucellate, basal or nearly so in single carpels, or axile in syncarpous ovaries. Fruit various, indéhiscent (a capsule in Barbeuia). Seed with a crustaceous or membranaceous testa (arillate in Barbeuia); perisperm copious to lacking in the mature seed; embryo curved.
The foliar theory of the stem, the application of which has been restricted to the pteridophytes, is now extended to the spermatophytes and the vasculature of the primary stem is viewed as a sympodium of foliar traces. Several new terms have been coined for the description of the primary vasculature; these include terms for vascular reticula and sympodia and two new conventions, the interleaf articulation ratio and interleaf articulation spacing. The patterns of primary vasculature in 20 Chenopodiaceous taxa have been re-described using a synoptic descriptive style. Based on the primary vasculature, within the Chenopodiaceae, two clear-cut groups have been recognized: (1) a Trioid vascular group, with 3-traced leaves and a median composite double trace, or taxa having such an ancestry; and (2) a Monoid vascular group, comprising taxa with 1-traced leaves and a composite double trace, or with this ancestry. The first group comprises the tribes Beteae, Chenopodieae, Atripliceae and probably the Polycnemeae and Corispermeae. The second group comprises the tribes Salsoleae, Suaedeae, Salicornieae and Camphorosmeae. In both the groups, reticulate and open vasculature are found, the latter being the derived state; the open vasculature derived from 3-traced ancestry is found to be different from that derived from 1-traced ancestry. These two groups differ from the subfam. Chenopodioideae (Cyclolobeae) and Salsoloideae (Spirolobeae), the groups identified on the basis of the cycloid/spiroid embryonic types. They match well with the groups identified from the chloroplast DNA analysis and appear to have distinct adaptive strategies; the first with modified/accrescent bracts, and the second with modified/accrescent perianth lobes. The findings from the primary vasculature therefore support the re-circumscription of the two subfamilies Chenopodioideae and Salsoloideae and the transfer of the tribes Camphorosmeae and Salicornieae to Salsoloideae. The processes involved in the diversification of primary vasculature in the Chenopodiaceae have been: changes from spiral to opposite phyllotaxy, reduction in the number of vertical rows of leaves, closed to open vasculature, non-storied to storied reticula, asymmetric to symmetric reticula, change in the loci of vascular articulations from the contributory arms to terminal arm of the composite trace, and wedged-sagittate to entire-acute base of reticula. Development of open vasculature from closed vasculature probably took place several times and followed independent lines. Therefore, many tribes in the family may be paraphyletic. Evolution of distichous sympodia from monostichous sympodia and vice versa, as proposed by earlier authors have been refuted. Strong correspondence of inference emerging from analysis of chloroplast DNA and primary vasculature refutes the probability of a protostelic origin of the eustele. It is argued that an atactostelic condition might have been ancestral, which gave rise to the protostelic condition on the one hand, and on the other to the eustele. The angiosperm leaf is considered as a composite organ formed by the syngenesis of two or more leaves/leaf lobes from different nodes, the details of which remain to be determined. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 143, 337–374.
