海南铜铁岭低地雨林蕨类植物区系及其特点

对海南铜铁岭热带低地雨林地区的蕨类植物区系进行了研究,结果表明铜铁岭共有蕨类植物117种,隶属40科、71属.含6种以上的科有水龙骨科、金星蕨科、铁角蕨科、叉蕨科、陵齿蕨科、膜蕨科和凤尾蕨科,它们是组成铜铁岭蕨类植物的优势科.根据植物的现代地理分布,本区的蕨类植物属和种的分布区类型中热带成分分别占非世界分布的95.31%和75.21%,说明了该地区蕨类植物区系与热带植物区系有着广泛的联系,热带性较强;本区蕨类植物大多数是林荫湿生或附生类型.七指蕨种群是该区珍稀蕨类植物,应该加强保护.     

GEMMIFEROUS FERN GAMETOPHYTES—VITTARIACEAE

Approximately 10 % of all fern species reproduce vegetatively in the gametophytic stage by means of gemmae. Gametophyte morphologies in these species depart radically from the commonly figured heart-shaped type and expand considerably the opportunities for physiological and morphological studies utilizing fern gametophytes. Original observations on four species of vittarioid ferns are presented and compared with earlier observations on gametophytes of this family. Vittarioid gametophytes grow from a discontinuous marginal meristem which results in a much branched thallus of indeterminant growth. Aerial branches of the gametophytes terminate in gemma production, which proceeds by a regular and predictable sequence of events. The sequence may differ considerably among species but is remarkably constant within species. Archegonia are produced on short ventral branches, and antheridia are produced primarily on germinating gemmae. Ananthacorus angustifolius is the only known member of the Vittariaceae which does not produce gemmae and is considered to represent the primitive condition. In this species antheridia are scattered over the thallus, suggesting that a change in the mode of control of antheridium production may have evolved in the family along with gemma production.     

云南哀牢山地区森林附生维管植物多样性及区系特征

附生植物作为山地森林生态系统中重要的结构性成分,在维持森林生态系统生物多样性格局、水分和养分循环等方面发挥着重要作用。本文通过野外调查、标本查阅并结合相关文献,对云南哀牢山地区附生维管植物物种组成及分布进行了系统研究。结果显示,哀牢山地区附生维管植物共有23科83属218种,其中附生蕨类和兰科植物最丰富。附生蕨类有34属93种,以附生-石生蕨类生活型占优势,其中水龙骨科17属62种,占附生蕨类的66.67%,瓦韦属(Lepisorus)和石韦属(Pyrrosia)分别有13种和10种。附生兰科植物有26属65种,其中石斛属(Dendrobium)和石豆兰属(Bulbophyllum)分别有12种和8种。该地区附生维管植物属的分布具有明显的热带性质并以热带亚洲分布居多。附生植物生长于生境因子变化剧烈、资源有限的林冠,对环境变化敏感,极易遭受破坏且破坏后难以恢复,不少附生植物具有很高的药用、观赏等价值。因此,应加强对附生维管植物这一特殊类群的保护。     

Epiphytism in ferns: diversity and history

As for other vascular plants, numerous adaptive strategies have been selected in epiphytic ferns in order to survive in a constraining and desiccating environment and thus to prevent dehydration and/or to access to water and nutrients. Here we present some of the specializations that allow ferns to survive in this particular habitat. Some of the most spectacular epiphytic specializations are observed in the Polypodiaceae family, involving humus-collectors which entrap humus in specialized organs, and ant-plant mutualism strategies. We then address the question of epiphytism in an evolutionary context. There is little fossil evidence of vascular epiphytes. Inferring the evolution of epiphytism in extant ferns shows that diversification of major living epiphytic groups mostly occurred in the Tertiary. Finally, we focus on the Hymenophyllaceae family which provides an original example of hygrophilous epiphytic strategy that is unique in vascular plants. To cite this article: J.-Y. Dubuisson et al., C. R. Biologies 332 (2009).     

A SURVEY FOR 1,3,6,7-TETRAHYDROXY-C-GLYCOSYLXANTHONES EMPHASIZING THE “PRIMITIVE” LEPTOSPORANGIATE FERNS AND THEIR ALLIES

A survey for 1,3,6,7-tetrahydroxy-C-glycosylxanthones of representative species within the primitive vascular plants, emphasizing the leptosporangiate ferns, has indicated a limited distribution of these compounds within three leptosporangiate families: Hymenophyllaceae, Aspleniaceae and Marsileaceae. In the Hymenophyllaceae the distribution of these compounds appears to be a useful criterion for segregating species of Mecodium from other species of Hymenophyllum (sensu lato) and suggests that the tubulate vs. the valvate indusial condition may not be an ideal character for separating all species of Hymenophyllum (s.l.) from those of Trichomanes (s.l.). These compounds appear useful for delimiting several species of Elaphoglossum section Pachyglossa and support a relationship among the Aspleniaceae, Athyriaceae, and Elaphoglossaceae. Their presence in Marsilea also raises questions as to the origin of this group of plants.     

Morphological innovation,ecological opportunity,and the radiation of a major vascular epiphyte lineage

The emergence of angiosperm‐dominated tropical forests in the Cretaceous led to major shifts in the composition of biodiversity on Earth. Among these was the rise to prominence of epiphytic plant lineages, which today comprise an estimated one‐quarter of tropical vascular plant diversity. Among the most successful epiphytic groups is the Polypodiaceae, which comprises an estimated 1500 species and displays a remarkable breadth of morphological and ecological diversity. Using a time‐calibrated phylogeny for 417 species, we characterized macroevolutionary patterns in the family, identified shifts in diversification rate, and identified traits that are potential drivers of diversification. We find high diversification rates throughout the family, evidence for a radiation in a large clade of Paleotropical species, and support for increased rates of diversification associated with traits including chlorophyllous spores and noncordiform gametophytes. Contrary to previous hypotheses, our results indicate epiphytic species and groups with humus‐collecting leaves diversify at lower rates than the family as a whole. We find that diversification rates in the Polypodiaceae are positively correlated with changes in elevation. Repeated successful exploration of novel habitat types, rather than morphological innovation, appears to be the primary driver of diversification in this group.     

浙江凤阳山-百山祖自然保护区蕨类植物区系研究

通过对凤阳山--百山祖自然保护区蕨类植物野外资源调查及区系分析,可以认为,凤阳山--百山祖保护区共有蕨类植物39科、79属、249种(含变种),主要科为鳞毛蕨科、水龙骨科、金星蕨科、蹄盖蕨科和膜蕨科;主要属为鳞毛蕨属、复叶耳蕨属、铁角蕨属、蹄盖蕨属和瓦韦属,其中以鳞毛蕨属和复叶耳蕨属分布相对集中。属的分布类型以热带成分为主,种以东亚分布类型和中国特有种为主,并含有72种中国特有和珍稀蕨类植物。     

The Exploitation and Utilization of Lycophyte and Fern Resources in Xishuangbanna,Yunnan

Xishuangbanna lies in the south of Yunnan. The composition and distributive regulation of lycophytes and ferns in Xishuangbanna are studied in this paper. As a result, 363 species of wild lycophytes and ferns which belong to 76 genera and 31 families are found in this area. The six species rich families are Polypodiaceae, Athyriaceae, Thelypteridaceae, Aspleniaceae, Pteridaceae and Selaginellaceae. The geographical distribution of the species shows that this flora mainly consists of Tropical Asia elements. Terrestrial species are the richest of this flora, followed by epiphytic and lithophytic species. The lycophytes and ferns resources of Xishuangbanna are abundant. However, the exploitation and utilization of this group of plants are ignored. This study investigated lycophytes and ferns resources of Xishuangbanna. Medicinal, edible and ornamental ferns in Xishuangbanna have been clearly researched and their utilization and protection have been discussed.     

Cainozoic ferns and their distribution

The phytogeographic distribution of Cainozoic ferns is reported based upon a critical re-appraisal of the macrofossil and mesofossil record also taking account of evidence from a few highly diagnostic spores. Well-documented circum-Arctic Cainozoic floras show ferns (Woodwardia, Onoclea, Osmunda, Coniopteris and to a lesser extentAzolla) distributed around the pole to very high paleolatitudes. Some ferns are shared between the mid-paleolatitudes of North America and Europe as would be predicted from the distributions of other biota. Evidence for the composition of Cainozoic fern floras is minimal in some regions (e.g., Antarctica, Central and South America, Africa, India, South East Asia), so the absence of fern fossils from these areas has no biogeographical significance. Matoniaceae were abundant in the preceding Mesozoic. However, the absence of Cainozoic macrofossils, and the fact that no CainozoicMatonisporites spores areMatonia-like, indicates that Matoniaceae had attained their modern relict distribution by, or very early in, the Cainozoic. The important Mesozoic families Marattiaceae and Dipteridaceae are also not represented by Cainozoic macrofossils. They probably also showed Cainozoic restriction but spores are not sufficiently diagnostic to enable testing of this hypothesis. Other ferns, which were also important in the Mesozoic (e.g., Dicksoniaceae, Gleicheniaceae), have patchy, equivocal, or inadequately published Cainozoic records. The dispersed spore record may provide an opportunity to track Cainozoic Gleicheniaceae but this approach is not without problems. Most well-represented Cainozoic fern families, genera and subgenera show widespread Cainozoic ranges, typically with considerable range extensions over their living relatives, both onto other continents and north and south to higher paleolatitudes. These include Schizaeaceae (Lygodium, Anemia, and the extinctRuffordia), Osmundaceae (Osmunda), Pteridaceae (Acrostichum), Thelypteridaceae (Cyclosorus), Lophosoriaceae (Lophosoria), Cyatheaceae (theCnemidaria/Cyathea decurrens clade) and the heterosporous water fernAzolla (Azollaceae). A few well-represented ferns show Cainozoic distributions similar to those of the present day (e.g.,Salvinia [Salviniaceae] andCeratopteris [Pteridaceae] (the latter by the Neogene and based only on spores]) but even these had slightly broader ranges in the Cainozoic. Some Cainozoic ferns have apparently local distributions, e.g.,Blechnum dentatum (Blechnaceae) in Europe; and others are so far represented at only one or few sites, e.g.,Dennstaedtiopsis (Dennstaedtiaceae),Botrychium (Ophioglossales),Grammitis (Grammitidaceae), andMakotopteris andRumohra (Dryopteridaceae). Cainozoic fossils assigned toDryopteris (and some other dryopteroids) require revision along with those of Thelypteridaceae, the latter having high potential to provide useful paleobiogeographic evidence, at least of theCyclosorus group. Cainozoic records of Hymenophyllaceae and Polypodiaceae are here considered unconfirmed.     

浙江省凤阳山自然保护区蕨类植物区系的研究

经野外调查和资料整理已知凤阳山自然保护区共有蕨类植物37科74属196种和7变种。主要科为鳞毛蕨科、水龙骨科、金星蕨科、蹄盖蕨科、铁角蕨科、卷柏科、膜蕨科,主要属为鳞毛蕨属、铁角蕨属、卷柏属、复叶耳蕨属、瘤足蕨属、凤尾蕨属、瓦苇属。分布区类型以世界分布和泛热带分布科、泛热带分布属、东亚分布种为主,表现出亚热带向暖温带过渡的特点。与邻近6山蕨类植物区系相似性系数的比较表明,与凤阳山蕨类植物区系亲缘关系最近的是浙江九龙山。凤阳山共有57种中国特有蕨类,有较高的保护价值。     

Study of the independent gametophytes found on Jeju Island in South Korea and the first record of the obligate independent gametophyte of Antrophyum obovatum Baker

Fern gametophytes have often been neglected in research; however, studies on gametophytes are crucial for a better understanding of the evolution of ferns. During their life cycle, some gametophytes produce large and long‐lived populations without producing sporophytes and reproduce independently through asexual means, such as through the formation of gemmae. In this study, we investigated independent gametophytes on the Jeju Island of Korea, which was located on the land bridge between East China and Japan during the glacial periods. Fourteen gametophyte populations were collected from seven sites, of which 13 populations were clearly identified as belonging to four fern species known to occur in Jeju Island with BLAST searches using rbcL and trnL‐F sequences. Surprisingly, the last remaining population constituted undescribed taxa in Korea. We presented the first report of the independent gametophytes of Antrophyum obovatum Baker which has not been previously recorded in Korea. It has been supposed that many ferns sought suitable habitat throughout the land bridge between China and Japan. However, Jeju Island might be unsuitable for vittarioid ferns that prefer a tropical or subtropical environment. Consequently, only two species of vittariod ferns (A. obovatum and Haplopteris flexuosa (Fée) E.H. Crane) in the form of a gametophyte and sporophyte, respectively, exist on Jeju Island. Therefore, this gametophyte population must be protected and managed from a conservation perspective. In the case of the independent gametophyte of Hymenophyllum wrightii Bosch, haplotype analysis was conducted based on the rbcL sequences and the result supported that the North American populations were migrated from Japan through land bridge during the glacial periods and Jeju populations were recently established by long‐distance dispersal of the Japanese populations.     

Gametophyte ecology and demography of epiphytic and terrestrial tropical ferns

Factors that influence the distribution of ferns are poorly understood and likely reflect the ecology of both the sporophyte and the gametophyte generation. Little study has been done on the ecology of the gametophyte generation, especially in regard to tropical species. The goal of this study was to examine demography and the influence of light and disturbance on the distribution of the gametophytes of several tropical epiphytic, hemiepiphytic, and terrestrial fern species. Through a series of observational and experimental studies, we found that increased terrestrial gametophyte density and richness were related to both increased light and disturbance. By contrast, increased light had no influence, and increased disturbance negatively affected epiphytic density. Over a 25-mo demographic study, epiphytic and hemiepiphytic species had significantly greater longevities and lower recruitment rates than terrestrial species. Such unique strategies may have evolved in response to different disturbance regimens between the two habitats. Terrestrial species encounter and are adapted to more frequent disturbance and have invested in rapid gametophyte growth and recruitment. Epiphytic species may be more influenced by bryophyte competition, and in habitats of relatively low disturbance, they have invested in greater size and longevities. In such systems, gametophytes are able to survive for years waiting for favorable recruitment conditions.     

海南尖峰岭自然保护区蕨类植物区系分析

对海南尖峰岭国家级自然保护区的蕨类植物区系进行了分析。结果表明：自然保护区内共有蕨类植物165种,隶属于41科84属,优势科有7科,分别为水龙骨科、铁角蕨科、金星蕨科、蹄盖蕨科、叉蕨科、膜蕨科、鳞毛蕨科,含5种以上的优势属有7属,分别为铁角蕨属Asplenium、卷柏属Selaginella、观音座莲属Angiopteris、鳞始蕨属Lindsaea、凤尾蕨属Pteris、短肠蕨属Allantodia、鳞毛蕨属Dryopteris;根据植物的现代地理分布,本区蕨类植物科、属、种的热带成分分别占非世界分布的96.6%、90.4%、72.2%,表明本区蕨类植物区系具有较强的热带性质;本区蕨类植物的属内种类贫乏,含1种的属占63.1%,含2～3种的属占21.4%;生态类型多样,主要有土生蕨类、石生和附生蕨类;苏铁蕨Brainea insignis、水蕨Certopteris thalictroides、金毛狗Cibotium barometz、桫椤Alsophila spinulosa、黑桫椤Gymnasphaera podophylla、大叶黑桫椤Gymnasphaera gigantea是本区国家重点二级保护珍稀濒危蕨类植物,应采取措施加强保护。     

云南蕨类植物的物种多样性和区系组成

在一定实地调查和分类的基础上,采用统计分析及区系地理分析法,对云南地区蕨类植物进行研究。结果表明:云南地区共有蕨类植物60科193属1 530种(包括变种和变型),科、属、种分别占中国蕨类植物科总数的58.8%,属的83.9%和种的95.2%;在这60个科中含30种以上的有13个,含5个属以上的有11个,分别占该蕨类植物区系属、种数的56.5%和79.2%,特别是鳞毛蕨科、蹄盖蕨科、水龙骨科和金星蕨科,这4个科共拥有70属761种,分别占总属数、总种数的36.3%、49.7%;193属中含30种以上的有11个,分别占总属、总种数的5.7%和41.7%,最具优势的是鳞毛蕨属和耳蕨属、蹄盖蕨属、铁角蕨属、卷柏属,这5个属共有403种,占总种数的26.3%;该区系中无云南特有科,但具有4个亚洲特有科:雨蕨科、稀子蕨科、柄盖蕨科和骨碎补科;该区系以热带、亚热带性质为主,科的区系成分中热带亚热带分布的科占66.6%,热带成分的属有112个,占68.7%(除世界分布类型);该区系是东亚地区蕨类植物区系的重要组成部分,东亚分布31属和中国特有分布6属,分别占总属数(除世界分布属外)的19.0%和3.7%;该地区蕨类植物区系与西藏、台湾具有共同的区系起源和物种分化形成的背景,属的相似性系数约为70%,种的相似性系数约为30%,均起源于热带亚热带地区;属的热带区系成分与温带区系成分所占比例分别为68.7%和27.6%,存在一定的区系过渡性;该区系科的分化强度为3.2,属的分化强度为7.9,在科、属水平上均表现出较强的区系分化特征。     

Exploring the pteridophyte flora of the Eastern Afromontane biodiversity hotspot

In this review, we explore our current understanding of the fern and lycophyte diversity occurring in the Eastern Afromontane Biodiversity Hotspot (EABH). The review explores the species diversity of this region in the context of the Afromadagascan pteridophyte diversity based on an exhaustive species list assembled in the synopsis of Afromadagascan pteridophytes published by Roux in 2009. The list was updated by incorporating recent progress in our understanding of the taxonomy and phylogeny of these plants. Evidence for a distinct pteridophyte flora occurring in the East African mountain region was discovered using ordination and clustering analyses. This EABH floras shares links to other Afromadagascan pteridophyte floras such as the one in the tropical lowland forests of central and western Africa. These floras share the dominance of species that preferably occur in humid climates whereas other African pteridophyte floras tend to contain a higher proportion of xeric adapted ferns. The phylogenetic composition of the EABH pteridophyte flora was assessed by comparing global versus local proportion of orders, families, and genera. This analysis revealed distinct patterns that are partly caused by the radiation of Blotiella and Triplophyllum besides selective colonization of species pre-adapted to Afromadagascan climates. In situ speciation in the East African tropical mountains may have contributed to the global diversity of widespread genera such as Asplenium and Pteris. In summary, this is the first comprehensive attempt to assess the pteridophyte diversity of the East African mountains providing the framework for future studies on their conservation, ecology, and evolution.     

雅鲁藏布江大拐弯地区蕨类植物科属区系特征分析

雅鲁藏布江大拐弯地区蕨类植物区系共含４５科、１０８属。主要科为鳞毛蕨科Ｄｒｙｏｐｔｅｒｉｄａｃｅａｅ（８０／５,种数／属数）、水龙骨科Ｐｏｌｙｐｏｄｉａｃｅａｅ（６５／１４）、蹄盖蕨科Ａｔｈｙｒｉａｃｅａｅ（４５／１１）、铁角蕨科Ａｓｐｌｅｎｉａｃｅａｅ（２３／３）、中国蕨科Ｓｉｎｏｐｔｅｒｉｄａｃｅａｅ（１９／６）、金星蕨科Ｔｈｅｌｙｐｔｅｒｉｄａｃｅａｅ（１８／９）、凤尾蕨科Ｐｔｅｒｉｄａｃｅａｅ（１３／２）、卷柏科Ｓｅｌａｇｉｎｅｌａｃｅａｅ（１２／１）和膜蕨科Ｈｙｍｅｎｏｐｈｙｌａｃｅａｅ（１１／３）。主要属是耳蕨属Ｐｏｌｙｓｔｉｃｈｕｍ,鳞毛蕨属Ｄｒｙｏｐｔｅｒｉｓ,铁角蕨属Ａｓｐｌｅｎｉｕｍ,蹄盖蕨属Ａｔｈｙｒｉｕｍ等系统发育上较高级的类群;无典型的特有属,可认为它是随青藏高原隆起而形成的较年轻的蕨类区系。其热带成分科属虽多（科占６２２％,属占６７６％）,但优势科、优势属均为广布类型。本区蕨类植物的起源是古老的热带亚洲成分。     

On the spore ornamentation of the microsoroid ferns (microsoroideae,polypodiaceae)

Journal of Plant Research - Microsoroideae is the third largest of the six subfamilies of Polypodiaceae, containing over 180 species. These ferns are widely distributed in the tropical and...     

Antheridiogen production and response in Polypodiaceae species

Antheridiogen chemicals secreted by living fern gametophytes have been shown to influence production of male gametangia and thus mating systems in a large number of terrestrial fern species. Antheridiogens have not previously been thought to be prevalent in the Polypodiaceae, a large family composed mostly of tropical epiphytes. This study presents bioassay methods more sensitive than previously used to detect antheridiogen and demonstrates that antheridiogens are also operative in the Polypodiaceae and in epiphytic species. Seven species in six genera (Campyloneurum angustifolium, C. phyllitidis, Lepisorus thunbergianus, Microgramma heterophylla, Phlebodium aureum, Phymatosorus scolopendria, and Polypodium pellucidum) were tested for the presence of an antheridiogen system. All species tested except P. aureum were induced to produce antheridia precociously by their own antheridiogen and by that of Pteridium aquilinum (APt). Phlebodium aureum responded to APt and promoted antheridium formation in Onoclea sensibilis but did not respond to its own antheridiogen. Spores of all species except P. aureum were induced to germinate in darkness by antheridiogen of the same species and by APt and to form antheridia in the dark, further enhancing the possibility of intergametophytic mating.     

Contrasting environmental and regional effects on global pteridophyte and seed plant diversity

Pteridophytes (ferns and fern‐allies) represent the second‐largest group of vascular plants, but their global biogeography remains poorly studied. Given their functional biology, pteridophytes are expected to show a more pronounced relation to water availability and a higher dispersal ability compared to seed plants. We test these assertions and document the global pattern of pteridophyte richness across 195 mainland and 106 island regions. Using non‐spatial and spatial simple and multiple regression models, we analyze geographic trends in pteridophyte and seed plant richness as well as pteridophyte proportions in relation to environmental and regional variables. We find that pteridophyte and seed plant richness are geographically strongly correlated (all floras: r=0.68, mainland: r=0.82, island floras: r=0.77), but that the proportions of pteridophytes in vascular plant floras vary considerably (0–70%). Islands (mean=15.3%) have significantly higher proportions of pteridophytes than mainland regions (mean=3.6%). While the relative proportions of pteridophytes on islands show a positive relationship with geographic isolation, proportions in mainland floras increase most strongly along gradients of water availability. Pteridophyte richness peaks in humid tropical mountainous regions and is lowest in deserts, arctic regions, and on remote oceanic islands. Regions with Mediterranean climate, outstanding extra‐tropical centres of seed plant richness, are comparatively poor in pteridophytes. Overall, water‐energy variables and topographical complexity are core predictors of both mainland pteridophyte and seed plant richness. Significant residual richness across biogeographic regions points to an important role of idiosyncratic regional effects. Although the same variables emerge as core predictors of pteridophyte and seed plant richness, water availability is clearly a much stronger constraint of pteridophyte richness. We discuss the different limitations of gametophytes and sporophytes that might have limited the ability of pteridophytes to extensively diversify under harsh environmental conditions. Our results point to an important role of taxon‐specific functional traits in defining global richness gradients.     

Developmental morphology of strap-shaped gametophytes of Colysis decurrens: a new look at meristem development and function in fern gametophytes

Background and Aims

The gametophytes of most homosporous ferns are cordate–thalloid in shape. Some are strap- or ribbon-shaped and have been assumed to have evolved from terrestrial cordate shapes as an adaptation to epiphytic habitats. The aim of the present study was to clarify the morphological evolution of the strap-shaped gametophyte of microsoroids (Polypodiaceae) by precise analysis of their development.

Methods

Spores of Colysis decurrens collected in Kagoshima, Japan, were cultured and observed microscopically. Epi-illuminated micrographs of growing gametophytes were captured every 24 h, allowing analysis of the cell lineage of meristems. Light microscopy of resin-sections and scanning electron microscopy were also used.

Key Results

Contrary to previous assumptions that strap-shaped Colysis gametophytes have no organized meristem, three different types of meristems are formed during development: (1) apical-cell based – responsible for early growth; (2) marginal – further growth, including gametophyte branching; and (3) multicellular – formation of cushions with archegonia. The cushion is two or three layers thick and intermittent. The apical-cell and multicellular meristems are similar to those of cordate gametophytes of other ferns, but the marginal meristem is unique to the strap-shaped gametophyte of this fern.

Conclusions

The strap-shaped gametophytes of C. decurrens may have evolved from ancestors with a cordate shape by insertion of the marginal meristem phase between the first apical-cell-based meristem and subsequent multicellular meristem phases. Repeated retrieval of the marginal meristem at the multicellular meristem phase would result in indefinite prolongation of gametophyte growth, an ecological adaptation to epiphytic habitats.