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Leaf anatomical characters and their value in understanding morphoclines in the Araceae.

II. Introduction

A new illustrated survey of the vegetative anatomy of the monocot family Araceae (Keating, 2003) has enlarged the potential for the use of this character set in phylogenetic analysis. The most promising characters, and some less promising, are discussed in anticipation of their being applied to phylogenetic analysis. The Araceae are currently understood to comprise 106 genera, divided among 9 subfamilies. Five of the subfamilies further divide the genera among 21 tribes (Appendix 1). The family includes more than 3000 species. Mayo et al. (1997) and Bown (2000) should be consulted for systematic and general overviews.

Observations of aroid leaf and petiole anatomy were first compiled by van Tieghem (1866), de la Rue (1866), and Dalitzsch (1886). Solereder (1919) and Solereder and Meyer (1928, 3:100-169) compiled data on approximately half of the currently accepted genera. In a long series of monographs on the family, Engler (e.g., 1905, 1911, 1912, 1915, 1920) always included anatomical observations. See French (1997) for a general review. With access to a broader generic sample of the family, French and collaborators in the 1980s published numerous studies describing a number of anatomical features of stems and reproductive organs. French (1997) reviewed this work and provided an overview of vegetative and reproductive anatomy of the family. The present review discusses the contribution of leaf and petiole characters to understanding the family's evolution.

The problem of defining usable characters in this family--or others--first involves determining characters that are diagnostic and reliable; i.e., characters that are genetically fixed and dependable indicators at the species and genus levels. Many useful characters have emerged for this purpose.

Other characters may be uninteresting or nondiscriminatory among groups of species within tribes and subfamilies but sometimes show subtle trends of variation across the family. In practice, for anatomical characters, genus or species diagnosis in this family must rely on a pattern of at least several characters, because few taxa are marked by only one or two clearly defined characters.

The potential for character analysis using stem and root materials is as large as the potential for leaves and petioles, but the sample size in this study (cf. Keating, 2003) is not as well developed.

III. Discussion of Anatomical Characters

Abbreviations and codes in parentheses refer to those used in Tables I and II.

A. LEAF VENATION

Among monocots, many leaves of aroid genera have perhaps the greatest tendency to resemble the venation patterns of dicots. Terminology as used in Table I was developed for diagnostic and evolutionary studies of dicot leaves (Hickey, 1979) and extended to net-veined monocots (LAWG, 1999). It should be emphasized that use of these terms does not imply homology between monocot and dicot patterns; they merely represent defined topographical states. Homologies are only assumed among specimens otherwise considered closely related, but developmental and positional equivalence must be demonstrated if homology is in question.

Using this terminology, now widely accepted by structural botanists, the majority of genera of Araceae exhibit pinnate venation. In such leaves, the lamina possesses a stout midrib that passes off secondaries at intervals on each side from base to apex. The same terminology is applied to the medial lobe of hastate, saggitate, and cordate leaves, which usually have three basal, acrodromous primaries, supplying the medial and basal lobes.

The term "midrib" is preferred over "midvein" because the midrib among monocots usually contains several to many discrete and scattered veins arising independently within the atactostele. Vascular bundles in midribs enter the lamina at intervals, individually or in groups, to form the secondaries. Unfortunately, confusion results from the traditional practice in many treatments of aroid genera to term lateral veins as "lateral primaries" (cf. Mayo et al., 1997). In LAWG (1999), the primary vein is dominant in pinnate leaves and normally synonymous with the midvein.

Venation patterns allow discrete characterization among aroid tribes even though evolutionary trends are not yet clear. Acrodromous (A) leaves have multiple ascending primaries and are scattered throughout the family in 9 suprageneric categories (Table I). Brochidodromous (B) leaves are found in 13 suprageneric categories, and the abmedial ends of the secondaries behave several different ways. There may be submarginal loops, or the brochidodromous arches may show tendencies toward straightening to form "collector" veins, as termed by aroid monographers, sometimes in several series. Eucamptodromous (E) leaves may show orthogonal, or ascending (acute and curved), secondaries.

Venation of intercostal areas also demonstrates systematic utility. Ultimate venation may consist of third-, fourth-, and fifth-order veins showing reticulate development, as in tribe Pothoeae and subfamily Lasioideae. Alternatively, as in tribe Philodendreae, veins that occupy intercostal areas mostly originate from the midrib and are called "primary intersecondaries." They are closely and evenly spaced and run parallel with the secondaries. In tribe Colocasieae, tertiaries mostly arise from the secondaries and curve to become parallel with the secondaries. They merge in the centers of intercostal space to form composite intersecondaries.

In several groups--tribes Pothoeae, Philodendreae, and Aglaonemateae--much variation exists, leaves of types A, B, and E being present and having a variety of higher-order domain development and shape. Those tribes offer perhaps the best opportunity for examining evolutionary trends. Venation trends were not specifically analyzed in Keating (2003).

B. LEAF STRUCTURE

Leaves are nearly always dorsiventral and hence rarely useful systematically, but the sharpness of differentiation varies from absent (Gymnostachys), to weak, to strong throughout the family. Midrib shapes are occasionally useful, for example, in the diagnostic presence of high adaxial ridges in Anthurium leaves, but midrib complexity is also predictably associated with size and weight of the lamina.

C. LAMINA EPIDERMAL CELLS

As seen in paradermal view, epidermal cells of the aroid genera observed are readily categorized for a given species and genus. The cells are linear (L) only in the case of the Australian genus Gymnostachys, the sole member of the basal-diverging lineage of the family. The usual cell outline is polygonal, and length:width ratios vary from 1:1 to 6:1, often in the same leaf. Anticlinal cell walls may be straight sided and therefore polygonal (P), undulate (U), or more deeply sinuous (S) (Table II). Usually a given species has one type, although two types may intergrade in one leaf. In a few genera, highly lobed cells are a surface phenomenon in which the interior anticlinal walls are straight-sided polygons. The phenomenon occurs in two subfamilies: Pothoideae tribe Monstereae (Alloschemone and Spathiphyllum); and Philodendroideae (Zamioculcas, tribe Zamioculcadeae and Callopsis, tribe Zantedeschieae).

Except in Gymnostachys, guard-cell pairs are randomly oriented (as is typically true for dicot leaves but not monocots) and mostly uniformly dispersed on leaf surfaces. Anomocytic stomata (a), where the neighboring cells are variable in number and adjacency patterns, are rarely found. They occur in Orontium (tribe Orontieae), in all genera of Lemnoideae, and two genera of Aroideae: tribe Areae.

The most common arrangement of adjacent cells in all other subfamilies and tribes is brachyparacytic (b2; see Table II). The pair of cells adjacent to the guard cells may nor be distinguishable from other epidermal cells except by their proximity pattern (neighboring cells), or they may be different in shape, usually narrower or more angular (subsidiary cells). It is often difficult to determine whether adjacent cells are neighboring or subsidiary, and both terms may apply even in the same field. Also, this stomate type may coexist on the same leaf with more elaborate types. They are called "brachyparatetracytic" (b4) if a second pair of subsidiary cells regularly occurs orthogonal to the first pair, across the poles of the guard cells. The term "brachyparahexactyic" (b6) is used when a third pair of subsidiary cells is added parallel to the first pair. Two subfamilies have a fourth pair of subsidiary cells (or more), for which the term "brachyparaoctocytic" (b8) is used. The term "amphibrachyparacytic" may a lso be applied in those cases, which are restricted to genera of subfamily Schismatoglottidoideae.

E. MESOPHYLL AND GROUND TISSUE

Cells are referred to as "compact" if little air space can be discerned and the parenchymatous cells are usually isohedral. The mesophyll of Gymnostachys qualifies, as does the ground tissue of many petioles and larger midribs (Table II). Type 1 mesophyll, the simplest aerenchyma, is applied to spongy mesophyll. The irregularly armed spongy cells have air spaces between them whose diameter is the same or less than the diameter of the cells themselves. Type 1 a is similar with regard to air space--cell diameter but has more clearly formed, short arms that extend and align with arms of adjacent cells and have end walls between them. Type 2 spongy cells have elongated arms contacting adjacent arms, and air spaces are two to four times the diameter of the cell bodies. This and subsequent types may apply to petiole and midrib ground tissue as well. Type 3 ground tissue has uniseriate, multicellular partitions between adjacent air spaces, forming a network around large air cavities. This type is common in midribs, lamina tissues, and petioles. Type 4 ground tissue, found in a few tribes, is a condition in which multiseriate partitions occur between several large air cavities.

Palisade parenchyma, absent in Gymnostachys, shows some variety but is not easily categorized. In about 15 genera, a few autapomorphies occur in the form of multiarmed palisade cells. They can be found in Pothoideae: Monstereae (3), Lasioideae (2); in Philodendroideae: Aglaonemateae (3) Zamioculcadeae (2), Spathicarpeae (1); and in Aroideae: Arisaemateae (1). Another unusual type, the T-shaped cell, is broadly in contact with the adaxial epidermis. These cells are found in Pothoideae: Pothoeae (Anthurium); in Philodendroideae: Culcasieae (Culcasia); and in Aroideae: Peltandreae (Arophyton). Because their distribution appears random according to well-supported schemes, they represent diagnostically useful character states, probably with no further analytical value.

F. VASCULAR BUNDLES

As seen in transverse section, these can be divided into about three types whose appearance is useful taxonomically (Table II). Type I is probably plesiomorphic and is characterized by large, generally circular bundles. Their xylem and phloem form semicircular strands adjacent to each other across a broad, straight boundary. There are usually 4 or more files of metaxylem, or between 10 and 20 xylem cells. Type II, smaller bundles, are more elliptic, and xylem and phloem tend to abut each other across a narrow boundary. Individual strand shapes are often irregular. Xylem cells are few and show no organization into ontogenetic files. Type III, also small bundles, are distinctive. They have narrow phloem strands adjacent to large, single, permanent protoxylem or metaxylem elements.

G. FIBERS

Many genera of aroids have some strengthening tissue associated with vascular bundles or ground tissue of midribs and petioles. Fibers form vascular bundle sheaths or caps over phloem, and sometimes xylem (Table II). Such strands are most frequently encountered when there is little or no collenchyma development.

Fibers appear to be most robustly developed in the subfamilies Gymnostachydoideae and Pothoideae, which include the greatest proportion of genera with ensheathed vascular bundles. The subfamily Philodendroideae also has frequent bundle caps and a few genera with ensheathed vascular bundles. Fiber caps occur as well in the subfamilies Schismatoglottidoideae and Aroideae: tribe Caladieae. The absence of fibers would appear to be apomorphic in the family.

H. SCLEREIDS

In the form of elongated trichosclereids, these sclerenchyma cells may be branched or unbranched. They are found in only 11 genera of the subfamily Pothoideae, mostly in the tribe Monstereae. Where found, they are conspicuous in leaf mesophyll, petiole ground tissue, and sometimes other organs. Trichosclereids, while not present in all of those genera, are exclusive to this subfamily. A number of studies have reported on the variety of trichosclereids in the family since Solereder and Meyer (1928, 3:100-169). See Seubert (1997) and Keating (2003) for recent reviews. Rare in the family are brachysclereids, occurring only in the genus Pothoidium.

I. COLLENCHYMA

Early work by Ambronn (1879-1881) described some of the variation in collenchyma to be found in the family, and Keating (2000) and Goncalves et al. (in press) were first to survey numerous genera for its occurrence. Collenchyma is often absent in genera that have welldeveloped fiber sheaths and caps. Where it occurs it forms bands (type B) at the periphery of midribs and petioles in the basal lineages. In later-diverging lineages, such as the subfamily Philodendroideae, bands may also become interrupted (type Bi), and later stranded. Strands may be nonaligned, or between peripheral vascular bundles (type Sb, in some philodendroid and schismatoglottidoid genera). Finally, only in the subfamily Aroideae are the strands aligned with peripheral vascular bundles (type Sv).

The subfamily Aroideae as understood here (see Appendix 1) is more narrowly circumscribed than the concept as found in Mayo et al. (1997) and can be delimited using collenchyma data. In a few cases (e.g., Scindapsus) bundle caps may occur as either fibers or collenchyma cells, sometimes in the same organ. Keating (2000, 2003) discusses possible trends of specialization of this tissue. It is possible that collenchyma originated from differentiation of ground tissue, especially the banded types, or that they share a homologous origin with lignified bundle cap elements (Keating, 2000).

J. LATICIFERS

Since Hanstein's (1864) study, most genera of aroids have been reported as having laticifers (French, 1988; Keating, 2003). They are always of the articulated type in this family and are absent or nonanastomosing ("non-a") in the early-diverging lines. A few genera (17) of the subfamily Aroideae bear anastomosing ("anas") laticifers. This character state has traditionally been invoked as evidence supporting their placement in one unified subfamily, the Colocasioideae (Engler, 1920; Grayum, 1990; Bogner & Nicolson, 1991). However, based on the French et al. (1995) cpDNA topology and ongoing studies by Chase et al. (pers. comm.) on rbcd and matK gene sequences, it appears that the Old World tribe Colocasieae and the mostly New World tribe Caladieae have evolved anastomosing laticifers independently and belong in nonadjacent tribes of the subfamily Aroideae. In the absence of molecular genetic data, it is interesting that no other structural markers, or groups of characters, are known that allow detection of the apparent paraphyletic relationship of these two tribes.

Pant and Kidwai (1966) have described laticifer ontogeny in the family, and that of ducts (see below). Much variation is found in their latex chemistry (Vagujfalvi, 1971; Fox & French, 1988), which is sufficient to be systematically useful.

The fact that both anas and non-a laticifers are found in different genera of tribe Colocasieae suggests a point from which to investigate their potential evolutionary relationships or trends.

K. SECRETORY DUCTS

In the four tribes where they occur (Table II), secretory ducts are large, circular, and lined with one or two layers of epithelial cells. They are usually found between vascular bundles and are not otherwise directly associated with them. Although secretory ducts have not been reviewed in detail for the family, their mucilaginous content has been reported on for Amorpho-phallus by Wakabayashi (1957). Grubert (1981) included the Araceae in a survey of angiosperm mucilage. Not all mucilage in the family is necessarily produced in ducts (e.g., Ulearum), and this topic is not currently well understood.

L. CRYSTALS

The Araceae are one of the few families that possess all five types of calcium oxalate crystals, at least two types being present in virtually every species, and usually in every organ. Early studies of four genera (Buscalioni, 1895-1896) were followed by studies adding more genera to the list of crystal-bearing genera. The most recent reviews are by Keating (2003, in press a). Along with raphides, druses and crystal sand occur nearly universally. Although there is some diversity among druse types, they have not yet been well characterized, and their systematic value is unknown. In a few genera styloids and prismatics are also found.

Among all crystal types, raphide bundles and their enclosing cells present the largest variation in this or any other family and have been subject to more intensive study (Keating, in press a). Virtually all genera have a simple, type 1 raphide cell, in which an irregularly shaped, thinwalled cell, somewhat larger than those of surrounding ground tissue, contains a single raphide bundle. That type is not further annotated in Table II. In addition to type 1, the leaf blades of most genera show greater variety in form of cell shape and raphide bundle type, each of which should be described separately. As one moves from blade, to petiole, stem, and root, the variety decreases, usually leaving only type 1 in the roots.

Using the coding from Table II, cells become wide (W) and contain broad crystal bundles, or elongate (E) where the cell is two to three times longer than the enclosed bundle. They are tubular (T) if the cell length is at least four times greater than the length of the enclosed crystal bundle. In elongated or tubular cells, there may be elongated bundles where the groups of crystals are oblique, overlapping, and sometimes helically arranged (Ov). Alternatively, in elongated cells, there may be two or more separate bundles of raphides. As found in the tribe Spathicarpeae and in the subfamily Lemnoideae, articulated tubes (Ta) are encountered where the idioblastic raphide cells are in contact and may attach end to end.

Spindle-shaped cells (Sb), where straight or tapering sides and rounded ends snugly enclose a crystal bundle, are found most frequently in the unisexual-flowered aroids. Probably related to these, and constituting the most structurally evolved crystal cell type, is a spindle-shaped cell bearing lignifield walls except for thin-walled papillae on the ends. Its occurrence is restricted to genera of the monoecious aroids. Named the biforine (B) by Turpin (1836), this cell easily discharges a stream of crystals from the cell tips when pressure is applied to the sides (Middendorf, 1983).

Given the broad array of crystal bundle and cell types for raphides in this family, clear trends of specialization might be expected, but they remain unexpectedly obscure (Keating, in press a). The low trend resolution of raphides in Table II should not prevent recognition of the diagnostic value of these idioblastic cells in combination with other generic and specific level characters.

IV. Conclusions

A survey of leaf and petiole characters occurring in the family suggests the following conclusions. Several characters, some of which are unexpected, are potentially polarizble. These include types or states of ground tissue, vascular bundles, fibers, trichosclereids, collenchyma, and laticifers.

Homoplasy will obscure the value of many clearly diagnostic states in phylogenetic analysis. Easily distinguished character states--e.g., epidermal cell shape, stomatal type, and raphide type--may be hierarchically shallow considered by themselves. That is, they provide an insufficient phylogenetic signal beyond a small group of species or genera that are believed to be related on other grounds.

The usual methodology of combining all of these characters in a familywide phylogenetic analysis would likely enhance ambiguity rather than good resolution. In the case of raphilde crystal cell expression, for example, finding a parsimonious route to character polarization may be impossible for most raphide states (Keating, in press a). The safest approach using anatomical data in this family would be to begin at the tribal level, genus by genus, gradually adding branches. It is hoped that the forthcoming anatomical compendium (Keating, 2003) will assist this process.

VII. Appendix 1: Revised Classification of the Genera of Araceae (Keating, in press b)

FAMILY ARACEAE Juss.

Subfamily Gymnostachydoideae Bogner and Nicolson

Gymnostachys R. E. Br.

Subfamily Orontioideae Mayo Bogner & P. C. Boyce

Tribe Orontieae R. Br.

Orontium L.

Tribe Symplocarpeae Engl.

Lysichiton Schott

Symplocarpus Salisb.

Subfamily Pothoideae Engl.

Tribe Pothoeae Bartl.

Pothos L.

Pedicellarum M. Hotta

Pothoidium Schott

Anthurium Schott

Tribe Monstereae Engl.

Holochlamys Engl.

Spathiphyllum Schott

Rhodospatha Poepp.

Stenospermation Schott

Scindapsus Schott

Rhaphidophora Hassk.

Anadendrum Schott

Monstera Adans.

Alloschemone Schott

Epipremnum Schott

Amydrium Schott

Heteropsis Kunth

Subfamily Lasioideae Engl.

Cyrtosperma Griff.

Lasimorpha Schott

Podolasia N. E. Br.

Lasia Lour.

Anaphyllum Schott

Urospatha Schott

Anaphyllopsis A. Hay

Pycnospatha Thorel.

Dracontium L.

Dracontioides Engl.

Subfamily Calloideae Endl.

Calla L.

Subfamily Philodendroideae Engl.

Tribe Philodendeae Schott

Montrichardia Cruger

Anubias Schott

Subfamily Philodendroideae Engl., continued

Tribe Philodendreae Schott. continued

Furtadoa M. Hotta

Philodendron Schott

Homalomena Schott

Tribe Zantedeschieae Engl.

Zantedeschia Spreng.

Callopsis Engl.

Tribe Stylochaetoneae Schott

Stylochaeton Lepr.

Tribe Zamioculcadeae Schott ex Engl.

Gonatopus Hook. f.

Zamioculcas Schott

Tribe Aglaonemateae Engl.

Nephthytis Schott

Anchomanes Schott

Pseudohydrosme Engl.

Aglaonema Schott

Aglaodorum Schott

Tribe Culcasieae Engl.

Culcasia P. Beauv.

Cercestis Schott

Tribe Spathicarpeae Schott

Bognera Mayo & Nicolson

Dieffenbachia Schott

Spathantheum Schott

Gorgonidium Schott

Synandrospadix Engl.

Gearum N. E. Br.

Spathicarpa Hook.

Asterostigma Fisch. & C. A. Mey.

Mangonia Schott

Taccarum Brongn.

Subfamily Schismatoglottidoideae R. Keating

Tribe Cryptocoryneae Blume

Cryptocoryne Fisch.

Lagenandra Dalz.

Tribe Schismatoglottideae Nakai

Phymatarum M. Hotta

Schismatoglottis Zoll. & Moritzi

Aridarum Ridl.

Piptospatha N. E. Br.

Bucephalandra Schott

Subfamily Lemnoideae Bab.

Spirodela Schleid.

Landoltia D. H. Les & D. J. Crawford

Lemna L.

Subfamily Lemnoideae Bab., continued

Wolffia Hark.

Wolffiella (Hegelm.) Hegelm.

Subfamily Aroideae Am.

Tribe Thomsonieae Blume

Amorphophallus Bl.

Pseudodracontium N. E. Br.

Tribe Caladieae Schott

Hapaline Schott

Syngonium Schott

Xanthosoma Schott

Chlorospatha Engl.

Ulearum Engl.

Filarum Nicolson

Zomicarpella Post & Kuntze

Caladiwn Vent.

Scaphispatha Brongn.

Jasarum G. S. Bunting

Zomicarpa Schott

Tribe Arisareae Dumort.

Ambrosina F. Bassi

Arisarum Mill.

Tribe Peltandreae Engl.

Peltandra Raf.

Typhonodorum Schott

Colletogyne Buchet

Carlephyton Jum.

Arophyton Jum.

Tribe Pistieae Rich

Pistia L.

Tribe Arisaemateae Nakai

Arisaema Mart.

Pinellia Ten.

Tribe Areae R. Br.

Typhonium Blume

Theriophonum Blume

Biarum Schott

Arum L.

Eminium (Blume) Schott

Dracunculus Mill.

Helicodiceros Schott

Tribe Colocasieae (Schott) Brongn.

Ariopsis Rojas

Alocasia (Schott) G. Don

Remusatia Schott

Colocasia Schott

Steudnera K. Koch

Protarum Engl.
Table I

Patterns of leaf venation in subfamilies and tribes of Araceae (L =
linear leaf, with mostly parallel primary veins; A = acrodromous; B =
brochidodromous; Bc = marginal or submarginal collector vein, presumably
originating from brochidodromous secondary loops; E = eucamptodromous;
IC = intercostal areas: lamina space between lateral secondaries; IS =
intersecondary vein: small tertiary-sized vein originating from midrib,
or originating as composite from merging tertiaries within an
intercoastal area and running parallel to secondaries)

Subfamily; Tribe Pattern

Bisexual-flowered aroids

GYMNOSTACHYDOIDEAE L

ORONTIOIDEAE
 Orontieae A, oblique secondaries
 Symplocarpeae E, orthogonal tertiaries or
 merging on secondaries
POTHOIDEAE
 Pothoeae A, B, E, variable, higher orders
 reticulate
 Monstereae B, E, collector veins, usually
 parallel ISs, oblique tertiaries
LASIOIDEAE B, E, intercostal areas reticulate
CALLOIDEAE E, ISs curved to secondaries

Unisexual-flowered aroids

PHILODENDROIDEAE
 Philodendreae A, B, E, ISs numerous and parallel
 Zantedeschieae (B), E, ISs parallel, secondaries
 orthogonal
 Stylochaetoneae A, E, secondaries merge with
 ascending primaries
 Zamioculcadeae Bc, IC areas and tertiaries
 irregular
 Aglaonemateae A, B, E, variable, higher orders
 reticulate
 Culcasieae E, ISs and tertiaries merging
 Spathicarpeae A, E, variable

SCHISMATOGLOTTIDOIDEAE
 Cryptocoryneae E, tertiaries ascending or
 orthogonal
 Schismatoglottideae E, parallel ISs collected at
 margin

LEMNOIDEAE A

AROIDEAE
 Thomsonieae Bc, IC areas with reticulate
 higher orders
 Caladieae A, B, tertiaries merge forming
 composite ISs
 Arisareae E, variable
 Peltandreae B, usually composite ISs formed
 of parallel tertiaries
 Pistieae A, parallel
 Arisaemateae B, submarginal loops
 Areae B, (E), submarginal or marginal
 loops, ascending secondaries and
 merging tertiaries
 Colocasieae B, tertiaries reticulate or
 parallel and merging forming
 composite ISs

Table II

Selected leaf characters in subfamilies or tribes of Araceae

(Epidermal cell shape: L = linear; P = polygonal, straight-sided
anticlinal walls; U = undulate anticlinal walls; S = sinuous anticlinal
walls. Stomata: a = anomocytic; p = parallel orientation;
b = brachyparacytic 2, 2-4, 2-6, 2-8 + = number of orthogonally arranged
subsidiary cells surrounding pairs of guard cells; - = absent. Ground
tissue: type 1, la, 2, 3, 4, in order of smaller to larger air cavities
[see text].

Vascular bundles: type I, II, III, in order of larger to smaller
[see text]; * = very reduced and irregular. Fibers: S = sheathing
vascular bundles; C = strands forming caps over phloem or phloem and
xylem; + = present; - = absent. Trichosclereids + = present; - = absent;
(+) = one species only. Collenchyma C = cap over phloem; B = banded;
Bi = banded interrupted; Sb = strands between outer vascular bundles;
Sv = strands opposite outer vascular bundles [on same radii] but not as
bundle caps; - = absent. Laticifers: non-a = non-anastomosing
anas = anastomosing - = absent. Ducts: + = secretory ducts lined with
epithelium present; - = secretory ducts lined with epithelium absent.
Raphides: W = wide cells; E = elongated cells; T = tubular cells;
[T.sub.a] = individual cells articulated end to end, forming articulated
raphide tube; S = coarse, styloid-like crystals; Ov = elongated bundles
of obliquely overlapping raphides; 2+ = 2 or more raphide bundles in a
single cell; Sb = thin-walled, spindle-shaped raphide ce ll;
B = biforine: lignified-walled, spindle-shaped raphide cell with
terminal thin walls, usually bearing papillae)

 Epidermal
Subfamily (number of genera); cell Ground
Tribe (number of genera) shape Stomata tissue

Bisexual-flowered aroids

GYMNOSTACHYDOIDE (1) L p, b2 1a

ORONTIOIDEAE (3)
 Orontieae (1) P a, b2 1, 3
 Symplocarpeae (2) P b2 ,

POTHOIDEAE (16)
 Pothoeae (4) P, U, S b2-6 1, 1a, 2
 Monstereae (12) P, U, S b2-6 1, 1a, 2

LASIOIDEAE (10) P, U, S b2-6 1, 2, 3, 4

CALLOIDEAE (1) P a, b2 3

Unisexual-flowered aroids

PHILODENDROIDEAE (27)
 Philodendreae (5) P, U b2-6 1, 2, 3, 4
 Zantedeschieae (2) P b2 1, 1a, 3
 Stylochaetoneae (1) P b2-6 1, 3
 Zamioculcadeae (2) P, U, S b2 1, 1a
 Aglaonemateae (5) P, U, S b6 1, 2
 Culcasieae (2) P, S, L b6 1, 2
 Spathicarpeae (10) P, U, S b2-6 1, 1a, 2, 3

SCHISMATOGLOTTIDOIDEAE (7)
 Cryptocoryneae (2) P b2-8 1
 Schismatoglottideae (5) P b2-8+ 1, 2, 3

LEMNOIDEAE(5) P, U, S - 1, 3

AROIDEAE (35)
 Thomsonieae (2) P, U, S b6 1
 Caladieae (11) P, U b2-6 1, 1a, 2, 3
 Arisareae (2) P, U, S b2 1, 2 3
 Peltandreae (5) P b2-4 3
 Pistieae (1) P b2 3
 Arismaemateae (2) P, U, S b2-6 1, 2
 Areae (6) P, U b2-4 1, 2, 3
 Colocasieae (6) P, U a, b2-6 1, 1a, 2, 3


Subfamily (number of genera); Vascular Tricho- Collen-
Tribe (number of genera) bundles Fibers Sclereids chyma

Bisexual-flowered aroids

GYMNOSTACHYDOIDE (1) I S - -

ORONTIOIDEAE (3)
 Orontieae (1) I C - -
 Symplocarpeae (2) I - - C, B

POTHOIDEAE (16)
 Pothoeae (4) I C, S (+) B, -
 Monstereae (12) I, II C, S + B, -

LASIOIDEAE (10) I, II C, S - B, -

CALLOIDEAE (1) I, II - - -

Unisexual-flowered aroids

PHILODENDROIDEAE (27)
 Philodendreae (5) I, II C, S - B, Bi
 Zantedeschieae (2) III - - Bi
 Stylochaetoneae (1) II - - B
 Zamioculcadeae (2) I, II C - B, -
 Aglaonemateae (5) I C, S - B, Bi, Sb
 Culcasieae (2) I C, S - B
 Spathicarpeae (10) I, II, III S, C - B, Bi

SCHISMATOGLOTTIDOIDEAE (7)
 Cryptocoryneae (2) II, III - - Sb
 Schismatoglottideae (5) II, III C - B, Bi

LEMNOIDEAE(5) * - - -

AROIDEAE (35)
 Thomsonieae (2) II, III - - Sv
 Caladieae (11) II, III C - Sv
 Arisareae (2) II, III - - Sv
 Peltandreae (5) II, III - - Sv
 Pistieae (1) II, III - - Sv
 Arismaemateae (2) II, III - - Sv
 Areae (6) II, III +, - - Sv
 Colocasieae (6) II, III - - Sv


Subfamily (number of genera);
Tribe (number of genera) Laticifers Ducts

Bisexual-flowered aroids

GYMNOSTACHYDOIDE (1) - -

ORONTIOIDEAE (3)
 Orontieae (1) non-a -
 Symplocarpeae (2) - -

POTHOIDEAE (16)
 Pothoeae (4) - +, -
 Monstereae (12) non-a, - +, -

LASIOIDEAE (10) - -

CALLOIDEAE (1) non-a -

Unisexual-flowered aroids

PHILODENDROIDEAE (27)
 Philodendreae (5) non-a +
 Zantedeschieae (2) non-a -
 Stylochaetoneae (1) - -
 Zamioculcadeae (2) - +, -
 Aglaonemateae (5) non-a -
 Culcasieae (2) non-a +
 Spathicarpeae (10) non-a -

SCHISMATOGLOTTIDOIDEAE (7)
 Cryptocoryneae (2) non-a -
 Schismatoglottideae (5) non-a +

LEMNOIDEAE(5) - -

AROIDEAE (35)
 Thomsonieae (2) non-a -
 Caladieae (11) anas -
 Arisareae (2) non-a -
 Peltandreae (5) non-a -
 Pistieae (1) - -
 Arismaemateae (2) non-a -
 Areae (6) non-a -
 Colocasieae (6) ana, non-a +, -


Subfamily (number of genera);
Tribe (number of genera) Raphides

Bisexual-flowered aroids

GYMNOSTACHYDOIDE (1) E: 2+

ORONTIOIDEAE (3)
 Orontieae (1) E: 2+
 Symplocarpeae (2) W, E, Sb

POTHOIDEAE (16)
 Pothoeae (4) E, T: Ov
 Monstereae (12) W, E, T: Ov, 2+

LASIOIDEAE (10) W, E, T: Ov, 2+

CALLOIDEAE (1) Sb

Unisexual-flowered aroids

PHILODENDROIDEAE (27)
 Philodendreae (5) W, E: Ov, 2+, Sb, B
 Zantedeschieae (2) W, E: Ov, Sb, B
 Stylochaetoneae (1) W, B
 Zamioculcadeae (2) W, E: Ov, 2+
 Aglaonemateae (5) W, E: Ov, 2+, B
 Culcasieae (2) W, E, T: Ov, 2+, Sb, B
 Spathicarpeae (10) W, E, T, Ta: Ov, 2+, B

SCHISMATOGLOTTIDOIDEAE (7)
 Cryptocoryneae (2) W, E: Ov, 2+, Sb
 Schismatoglottideae (5) W, E: Ov, B

LEMNOIDEAE(5) E: Ov, Ta

AROIDEAE (35)
 Thomsonieae (2) S, W, E: Ov, 2+, B
 Caladieae (11) W, E, T: Ov, 2+, Sb, B
 Arisareae (2) W, E: 2+
 Peltandreae (5) W, Sb, B
 Pistieae (1) Sb, B
 Arismaemateae (2) W, T: Ov, 2+
 Areae (6) W, E, T, Ta: Ov, 2+, Sb, B
 Colocasieae (6) W, E, T, Ta: Ov, 2+, Sb, B


V. Acknowledgments

My thanks to the organizers of this symposium, Dennis Stevenson and Ken Cameron, for the opportunity to present this work. This contribution is dedicated to the memory of William C. Dickison, more than an esteemed teacher and scholar, a generous friend.

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