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Ginger: plant's structure, general morphology, economic importance

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Zingiberaceae

Structure of the ginger plant

Gingers are monocotyledonous perennial herbs with fleshy rhizome that is sympodial branched ending in an erect shoot bearing leaves, flower or generally both. The rhizome is composed generally of distinct segment, may be short or long, stout or thin covered with distichously arranged scale leaves with an encircling insertion. It consists essentially of an axis bearing and its inflorescent are spirally arranged in primary bracts, each of which subtend a flower bearing cincinnus. The branches of gingers are developed from buds in the axils of scale leaves at the base of the erect shoot (Holttum, 1950). Compared to other species that has a presence of a real stem, gingers are replaced by a ‘pseudostem’ (Kress, 1990). Leaves are simple, with few to many distichously arranged blades, leaf sheath that are usually suborbicular or lanceolate to narrowly strap shaped, rolled longitudinally in the bud, glabrous or hairy with prominent midvein and complete margins (Jatoi et al., 2007). The sheath is replaced by a membranous ligule that can use for the identification of several genera. The ligules are usually black as found at the junction of the blade and sheath or the junction of the petiole and sheath.

Generally, flowers of gingers are bisexual, epigynous and zygomorphic solitary in the axils of bract or in cincinni, with or without secondary bracts. The flowers are also ephemeral that usually last for only a couple of hours to a day (Burtt, 1972; Smith, 1990). Calyx is tubular; that is usually slender corolla tube divided into three subequal- sized petals. Its ovaries are inferior and initially 3- loculed by may change to 1-or 3 loculed when mature. While its fruits are capsular, fleshy or dry, dehiscent or indehiscent, sometimes berry like. Seeds may be few or many, arillate; aril, often lobed or lacerate ( Baker 1892; Ghazantar and Smith 1982; Te- lin and Larsen 2000). Morphologically, they are easily identified by their vessel elements with distinct features, specifically roots (Wagner, 1977; Gevu et al,. 2017).

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Classification of Zingiberaceae

Traditionally, the family of Zingiberaceae is divided into four tribes: Alpinieae (leaves perpendicular to rhizome, lateral staminodes absent or small and fused to labellum), Globbeae (filament long exserted and arched, gynoecium unilocular), Hedychieae (leaves parallel to rhizome, lateral staminodes petaloid, not fused to labellum), and Zingiberaceae (style exerted past another and enveloped by elongate anther crest,) (Burtt & Smith, 1972).

Kress et al. (2002) using molecular sequence data, however, sampled 104 species in 41 genera representing Zingiberaceae four tribes in order to evaluate past classifications of the family, to identify morphological features that characterize the various clades detected by the molecular analyses, to evaluate the status of monotypic genera where possible, and to construct a new phylogenetic classification of the family. Believing that a revised classification is needed to better represent the new data on evolutionary relationship despite some congruence existing between the former and current phylogenetic results, they realigned the Zingiberaceae family into four subfamilies: [1] Siphonochiloideae, [2] Tamijioideae, [3] Alpinioideae, and [4] Zingiberoideae.

Philippine Zingiberaceae

There’s a wide variety in the monocot ginger family of Zingiberaceae that are present in the Philippines. The majority of Philippine gingers are found in Luzon while many remain undiscovered in the unexplored forest in Visayas and Mindanao (Hughes et al., 2015). Some Zingiberaceae plants grow as wild species in forests and in mountains. In Mindanao there’s a lot of High Mountain that needs to be explored because of the possibility of discovering new species and to better understand their distribution (Acma & Mendez, 2018). To date, there are 16 genera and over 111 species however, those are only the named species (Table 1) (Newman et al., 2004; Pelser et al., 2011). At present, there has been little taxonomic work on Philippine Zingiberaceae since Merrill’s magnum (1925) enumeration of flowering plants. Moreover, studies on the conservation ecology, distribution, and ethnobotany of the family are few and most are outdated.

Economic Importance of Gingers

Zingiberaceae, commonly known as gingers provides many useful products for culinary, medication, dyes, perfumery and ornamental horticulture field. Species of this family are known to produce commercial spices such, cardamom and turmeric (Poulsen, 1996). Young rhizome of Boesenbergia rotunda (L.) Mansf., has been utilized for a long period of time as a flavoring and popular for vegetables seasoning (Chahyadi et al.,2012). Another known species like Curcuma longa L. and Zingiber officinale Rosc. are used as food condiments and flavorings (Nurainas & Arbain, 2015). Also, it is a familiar aphrodisiac in folk medicinal uses, rhizome of ginger has been used to treat different conditions like diarrhea, stomach discomfort, mouth irritation, rheumatism, fungal infection and also serve as inti-inflammatory for wounds. (Chahyadi et al.,2012). Furthermore, B. rotunda rhizomes contains an active constituents against HIV-protease (Tewratakul et.al 2013) and exhibits anti-tumor and anti-mutagenic activities (Murakami et.al., 1994; Trakoontivakron et al., 2001; Tunchinda et al., 2002).

Ginger species are also cultivated for landscape proposes. Curcuma L. and Kaempferia L. species has unique and colorful properties that can be use as flowering pot plants, both indoors and in patio (Kuehny et al., 2002). Lastly, it constitutes a vital group of rhizomatous medicinal and aromatic plants characterized by the presence of volatile oils and oleoresins of export value and widely distributed in India, and in tropical and subtropical regions of Asia (specially Thailand, Indonesia and Malaysia) (Nicolaou et al., 2010).

Boesenbergia

General Morphology

Members of this genus are distinguished mainly by the two-ranked rather than spirally arranged bracts (distichous), boat-shaped bracteoles, apex to base sequence of flowering (determinate inflorescences), and strongly saccate or more or less entire labellum (Smith, 1987; Larsen et al., 1999; Mood et al., 2014). Presented in full knowledge the following account has many imperfections and it is clear that more filed study is needed on the following points; Anther dehiscence, fruit, variegation, and leaf- shoots (Smith, 1987)

Widely distributed in Indo Malaysia, Boesenbergia are small herbs of the forest floor with rhizome that are irregularly shaped, measuring c. 1 cm in diameter, its external anatomy is brown in colour and internally light yellow to white with multiple small bulb-like rhizomes surrounding the main rhizome. The pseudostem is up to c. 30 cm long, composed of leaf sheaths which can be longitudinally ridged, green, glabrous, margin hyaline. Leaves per pseudostem reach up to 5 to 9; petiole 9-18 cm, deeply channelled, green, glabrous; ligule slightly bilobed, lobes an extension of the hyaline margin, 2 mm long, slightly acute, protruding outward, green, glabrous; lamina elliptical or broadly ovate, c. 41- 61 Г— 20-21 cm, plicate, ventrally dark green, glabrous, dorsally lighter green, glabrous with a few hairs on the midrib, base rounded to cordate, sometimes asymmetric, apex acute to long acuminate. Inflorescence arising from the leaf sheath of a single bladed shoot or from the uppermost sheath of a tuft of leaves. It resembles Haplochorema K.Schum and Scaphochlamys Baker in its vegetative state (Smith, 1987).

Phylogenetic studies in Boesenbergia

Over the past several years, botanist and several taxonomists have been collecting molecular data from both the nuclear ITS and the chloroplast trnK/matK intron to produce a phylogeny of Boesenbergia. Chaiyoot (2007) produced a molecular phylogeny of Caulokaempferia using 23 taxa from Thailand including accessions of Boesenbergia. The results showed that Caulokaempferia is polyphyletic with two distantly related clades. Since a sample of the type species, Caulokaempferia linearis (Wall.) K.Larsen (= Monolophus linearis (Wall.) Wall.) was not included, no definitive conclusion was possible as to which clade should retain the name Caulokaempferia. Picheansoonthon (2008), using molecular data obtained from previous study and morphological characters of the flower color and capsule type, determined that the largest clade represented true Caulokaempferia while smaller clade was treated as a new genus: Jirawongsea. Moreover, based on Mood et al. (2014), Monolophus appeared to have been validly published with two species, one of which is the type of Caulokaempferia, this controversial information made an in depth nomenclatural study to understand why Monolophus had not been used in leu of Caulokaempferia.

Moreover, the results of Mood et al. (2014) showed that all trees from all analyses with a monophyletic Caulokaempferia (= Monolophus) and Boesenbergia. Additionally, both phylogenies placed all samples of Jirawongsea within Boesenbergia. The combined ITS and trnK/matK data analysis showed that Jirawongsea (labelled Boesenbergia in Fig. 1) are part of a strongly supported (BS = 100%) clade that includes B. rotunda and B. curtisii, which is nested within the monophyletic Boesenbergia (BS = 56%). These findings are consistent, whether ambiguously aligned ata are included or excluded from the analyses. Analyses of just the ITS or trnK/matK data partitions recover similar tree topologies.

Philippine Boesenbergia

Currently, there are only two species of Boesenbergia recorded in the country namely B. longipetiolata and B. macropoda which are both endemic (Newman et al., 2004; Pelser et al., 2011 onwards). The first Boesenbergia species recorded in the Philippines, B. longipetiolata (Fig. 2A), was first described by Ridley (1909) under Gastrochilus Wallich., a genus currently synonymized under Boesenbergia. Ridley (1909) noted that the reason why his description is very limited is because the collection H.N. Whitford, & J. Hutchinson 9110 from Zamboanga (which is apparently missing), is only represented by a single specimen with a single flower. With this, Ridley (1909) suggested that the only way to obtain good reproductive material is to cultivate them.

Since their discoveries in the early 1900’s, these two Philippine Boesenbergia species were never recollected. Interestingly, through the help of Co’s Digital Flora Website (wwww.philippineplants.org), a photograph of a possible species of Boesenbergia in Palawan was posted. The identity of this species, however, cannot be determined since the two described species has very limited information regarding their morphology, and the type specimens are to bad to acquire morphological characters especially on the reproductive parts.

Molecular Markers

Internal Transcribed Spacer (ITS)

Proven its usefulness in phylogenetic studies from a across range of taxonomic ranks, species to families (Schaal & Learn 1998; Sun et al., 1993., Hslao et al., 1995; Sun et al), the Internal Transcribed Spacer (ITS) region has been useful in elucidating major lineages of land plants (reviewed in Baldwin et al.,1998).With its ease in amplification and pros characteristics that allow it to be use for differentiation of closely related species the ITS is one of the most commonly used for Angiosperms (Droop, 2012) such as genus Boesenbergia. The prominence of this source of nuclear DNA sequence data is underscored by a survey of phylogenetic publications involving comparisons at the genus level or below, which reveals that of 244 papers published over the last five years, 66% included ITS sequence data. Perhaps even more striking is the fact that 34% of all published phylogenetic hypothesis have been based exclusively on ITS sequences (Alvarez et al., 2003).This reports, data and result just indicates that ITS is a very useful gene marker for identifying Plant Species. Moreover, its established record on its sequence data region according to Baldwin (1995), provide vital phylogenetic insights. Yet, the decision to use ITS loci is not purely based on its powerful bandwagon effect / sociological factors, but reiterate the long noted properties of ITS (Baldwin et al., 1995) namely (1) Biparental inheritance, this demonstrated how valuable this property is for revealing past cases of reticulation, hybrid speciation, and parentage of polyploids (Baldwin, 1992; Baldwin et al., 1995; Kim and Jansen, 1994; Rieseberg et al.,1990; Rieseberg and Soltis, 1991; Rieseberg and Wendel, 1993; Wendel et al., 1995). (2) Universality, White et al. (1990) described a set of primers that was useful for amplifying ITS sequences from most plant and fungal phyla.

Simplicity, because there are hundreds to thousands of nuclear rDNA repeats in plant genomes, they are more easily isolated than most low-copy nuclear loci, requiring little experimental expertise to successfully amplify. In plants, ITS sequences vary in length from approximately 500–700 bp in angiosperms (Baldwin et al., 1995) to 1500–3700 bp in some gymnosperms (Bobola et al., 1992; Germano and Klein, 1999; Liston et al., 1996; Maggini et al., 2000; Marrocco et al., 1996). (4) Intergenomic variability, ITS sequence variation levels are suitable for phylogenetic inference at the specific, generic or even family levels (Baldwin, 1992; Baldwin et al., 1995). (5) Low functional constraint, since the ITS sequences are removed via splicing during transcript processing, they would be subject to reasonably mild functional constraints, which in turn would offer a preponderance of nucleotide sites that would evolve essentially neutrally. The functionality of ITS is related to specific cleavage of the primary transcript within ITS-1 and ITS-2 during maturation of the small subunit (SSU), 5.8S, and the large subunit (LSU) ribosomal RNAs (Hadjiolova et al., 1984, 1994; Musters et al., 1990; Nashimoto et al., 1988; Veldman et al., 1981; van Nues et al., 1994). And (6) Intragenomic uniformity, It has long been recognized that multigene families in general and ITS sequences in particular may be subject to a phenomenon termed concerted evolution.

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