CYCADACEAE UPDATED (1999)
 D. J. DE LAUBENFELS

CYCAS
Cycas L., [Hort. Cliff. (1737) 482] Sp. Pl. (1753) 1188; Gen. Pl. ed. 5 (1754) 495.  -- Type species: Cycas circinalis L.

Short to tall palm-like trees with cylindrical often branched trunks, base sometimes eventually enlarged, not subterranean.  Leaves flat or both rows of pinnules raised to form a trough (secund). Pinnules undivided and entire, moe or less lanceolate, straight or curved either basally in most species orapically in others, sessile, decurrent, margins flat to revolute; neighboring pinnules averaging 2-4 mm apart in the broadest part of the leaf, but more dispersed basally amd more crowded apically (when the pinnules are angled apically they can touch one onother). Megasporophylls with or without teeth in the apical part, teeth up to c3 cm long but often only 1-2 mm long, usually increasing in length towards the acumen or all of the same size; from one to in some species as many as twelve and in all species to at least four ovules. 

    Distribution -- Twenty eight species from eastern Africa and Madagascar across India to southern China and Japan, across the larger and smaller tropical Asian islands to the Marshall Islands and Tonga, and along the northern and eastern coasts of Australia. 

    Habitat -- In moist to humid environments from the equatorial rainforest a short distance into the subtropics at low to moderate elevation.  Found in the understory of forests, particularly along streams or in open disturbed areas, often where the conditions are seasonal.  Probably establishing most commonly in open conditions but, because of their slow growth and long life, becoming overtaken by larger faster growing trees. 

    Notes -- Several problems attend the identification of species of Cycas and need to be considered.  This is partly due to the slow growth of these plants which may not present reproductive material for many years at a time.  As a result, many collections are sterile and the pollen structures for several species are not yet properly described.  Other problems arise from a natural variability and the large size of the leaves.

Cycas leaves vary a great deal with age and vigor of a plant. Because of their size or accessibility, the largest leaves are rarely collected.  Thus, whole leaves, when available in the herbarium, are frequently smaller than reported typical sizes.  The number and length of the pinnules also vary with age and vigor and furthermore are somewhat shorter towards the upper and lower part of the leaf.  The spacing of the pinnules also, varies from one end of the leaf to the other, loosely spaced basally and more or less crowded apically.  Collectors usually save only a portion of the leaf and different parts of the same leaf may appear from the same collection in different herbaria.  In spite of published reports of different spacing in various species, a careful study of specimens and all available published data on leaf size and number or pinnules representing nearly all species shows a remarkable degree of consistency in average spacing within a leaf.  Published data not conforming with this observation usually indicate a crowding or even overlap of pinnules which observation does not confirm (overlapping pinnules do not occur).  For example, Hill (1992) for media gives up to 150 pinnules on each side of a leaf but a maximum of 140 cm for the leaf less the petiole, that is less than one cm for each pinnule on the average, yet the pinnules are up to 10 mm wide at the widest part (and he has the median pinnules 13 mm apart).  His ophiolitica is “more crowded” than media and is so illustrated and yet the numbers provided indicate distinctly more space for the pinnules of the former than for the latter.  Pinnule spacing is seldom if ever a distinction for Cycas species.  Fortunately pinnule width is not particularly variable within a species.

Pinnule apices are often battered or missing in the herbaria, but in only a few species is the shape of the apex significant.  Probably all Cycas pinnules are originally apiculate.  These apiculate tips are often called acuminate which contrasts within the broad acuminate tips with an acumen over 1 cm long, which normally appear on pinnules over 15 mm wide.  As pinnules become narrower they become less lanceolate and the narrowest pinnules have a more or less rounded apex.

The midrib of the pinnules on immature leaves is usually weak, later becoming more prominent.  In some species it becomes equally or more prominent above, others below, while in a few it never becomes prominent.  The upper surface of the midrib may be more or less yellow but this condition is quite variable and appears to result from growing conditions.

The apex of the leaf often has a wedge or V-shaped gap between the last spreading pinnules while the rachis is terminated by no more than a tiny spur or a very reduced pinnule.  Equally often there is one pinnule bent into a terminal position.  Sometimes there may even be 2--3 or more progressively strongly reduced pinnules spreading laterally and a smaller one terminal.  Considerable variation is seen on adjacent leaves and although a progressive strong reduction of apical pinnules may be more common in such species as revoluta and taitungensis, it is by no means always present even in them.

The amount of narrowing of the base of a pinnule varies along a rachis.  It is greatest at the base of the leaf and may sometimes almost form a petiole.  Further apically the base is broader and more strongly decurrent.  Specimens representing portions of a leaf will obviously vary in this character depending on which part of the leaf from which they derive.

Much has been made by some authors over the leaf petiole where thorns may replace the pinnules or the petiole may be thornless.  Probably no species is totally thornless and leaves with some thorns can be seen growing on the same plant alongside thornless examples.  The tendency to few or no thorns is, however, a significant trait.  When the leaf base is cut off by a collector, as it usually is, this trait cannot be seen.  Or worse, the small part of a petiole remaining may have thorns but the missing part may or may not and the impression is therefore misleading.

Cycas ovules mature into a fruit containing a stony seed covered by a fleshy coat some 4--5 mm thick.  Immature undersized fruits are often collected and in all dried specimens the coat is reduced to a thin wrinkled covering which is usually present on herbarium sheets.  The whole thing including the coat is commonly referred to as a seed but collectors rarely specify which they have in mind, fresh or dried or without the coat, when they report “seed” size.  This confusion affects the reported seed size for many species.

Pollen cones of cycads are often difficult to obtain and they tend to disintegrate after shedding pollen.  Before shedding pollen they are compact but with shedding they elongate and thereby usually shrink in diameter (see Krempen, 1990, page 226, photo of pruinosa with both stages together).  When shedding, the upper microsporophylls often are reflexed basally.  Immature specimens when dried will shed pollen and immature specimens may well be collected and described.  The result is that the dimensions given for pollen cones are quite unreliable.

Other variable traits can be noted.  Pinnule margins are usually revolutely bent but the amount of bending varies from one specimen to another and perhaps with age.  Clearly, the narrower pinnules are more noticeably revolute.  The two rows of pinnules may be widely spread out making a flat leaf or they may approach each other to form a trough, but pressing the leaves may well obscure this variable.  Leaf glaucousness is not readily evident on dried specimens and is often a very inconstant character.  The number of ovules on a megasporophyll varies a great deal within a species and even within a cluster on a plant, while normally no more than one or two megasporophylls are included in a herbarium specimen.  The length of apical spines on fertile scales can vary quite a bit from the base to the apex of a pollen cone.

SUBDIVISIONS OF THE GENUS
Only limited attempts have so far been made to subdivide the genus Cycas, mostly by segregating one or two species from the rest.  Miquel (1843) contrasted revoluta (adding inermis in 1849) from the rest of the genus for linear revolute pinnules. Later (1868) he made this division more formal but without any group name, distinguishing revoluta by tomentose ovules.  Pilger (1926), also without any group names, separated the species with more than two ovules per megasporophyll (most of them) from those with two (two species).  Unfortunately his information was incorrect.  He further subdivided the first group into pectinate and not pectinate megasporophylls.  Schuster (1932) described three sections, giving them regional names.  His Asiorientales included only revoluta and has linear pinnules and cuneate microsporophylls, among other things.  His Indosinensis included two species, viz. siamensis and micholitzii, with bulbous trunk bases, linear lanceolate leaves, and sphenoid microsporophylls.  All the rest of the genus went into Lemuricae with subacuminate pinnules and acuminate microsporophylls.  Smitinand (1971) distinguished a monospecific section Stangerioides for micholitzii based on a subterranean trunk and apiculate microsporophylls.  He further separated his five other treated species into dentate or pinnatified margins of the apical part of the megasporophyll.  The sections Indosinensis and Stangerioides are included in the genus Epicycas. 

Recent suggested generic subdivisions continue to be less than satisfactory.  Dehgan and Yuen (1983), working with cultivated material, suggested dividing the genus into two groups based on the buoyancy of the seeds.  According to them three widespread species have buoyant seeds.  One of these is circinalis which most certainly does not have buoyant seeds.  Probably the material they studied was misidentified.  Although several species of Cycas do have buoyant seeds, various close relatives of these do not.  Dehgan (1987) proposed but did not describe groupings identified only by their type species.  All of his subgenera and sections have names inadmissible according to established taxonomic rules.  The use of subsections by Schuster and others will not be treated here because they add little to our understanding of the genus. 

Several distinctions are repeated in these suggested subdivisions of the genus and can be used in a formal set of subgenera.  Bulbous or subterranean trunks, pectinate or pinnatifid megasporophyll margins, along with certain other traits effectively segregate the various species heretofore included in the genus Cycas.  The bulbous underground base will be used to separate a new genus, Epicycas.  The remaining species are divided into four subgenera.

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