Taiwan

Bot. Bull. Acad. Sin. (2000) 41: 151-158

Peng and Sue Begonia taipeiensis, hybr. nov. in Taiwan

Begonia taipeiensis (Begoniaceae), a new natural hybrid in Taiwan

Ching-I Peng1,3 and Chian-Yi Sue2

1Institute of Botany, Academia Sinica, Nankang, Taipei, Taiwan 115

2Department of Biology, National Taiwan Normal University, Taipei, Taiwan 117

(Received August 12, 1999; Accepted January 5, 2000)

Abstract. A new natural hybrid of Begonia, B. taipeiensis, from northern Taiwan is described and illustrated. It grows on moist, rocky slopes on forest margins at 200-500 m elevation. Based on a comparison of morphology, geographical distribution, pollen stainability, seed set, cytological observations, and experimental crosses, we conclude that B. taipeiensis represents F1 progeny from natural hybridization between B. formosana (Hayata) Masam. [sect. Platycentrum (Klotzsch) A. DC.] and B. aptera Blume [sect. Sphenanthera (Hassk.) Warb.].

Key words: Begonia; Begonia aptera;Begonia formosana; Begonia taipeiensis; Hybrids; Natural hybridization; Taiwan; Taxonomy.

Seven species of Begonia were treated in the first edition of the Flora of Taiwan (Liu and Lai, 1977). Subsequently, Begonia lukuana (Liu and Ou, 1982), B. ravenii (Peng et al., 1988), B. fenchihuensis (Ying, 1988), B. austrotaiwanensis (Peng and Chen, 1990), B. tarokoensis (Lai, 1990), B. nantoensis (Lai and Chung, 1992) and B. hohuanense (Ying, 1995) were reported as new to this island. A total of 12 species of Begonia were recognized (Chen, 1993) in the second edition of the Flora of Taiwan. Peng and Chen (1991) documented the hybrid status and parentage of Begonia buimontana Yamamoto (pro species), which is restricted to elevations between 1,000 and 1,600 m in southern Taiwan. We present here a report of another naturally occurring hybrid of Begonia in the northern part of this island.

Begonia taipeiensis C.-I Peng, hybr. nov. TYPE: TAIWAN. Taipei Hsien: Wulai Hsiang, along trail to Hsiaoyi, ca. 3-5 km from Wulai. Abundant locally, forming a population ca. 1 m long 0.6 m wide on a moist rock, 24 50 N, 121 34 E, ca. 200 m alt. Field collection made on 16 Apr 1991; type specimens pressed from cultivated plants. Peng 13899 (holotype: HAST; isotypes: A, CAS, E, HAST, KUN, MO, PE, TAIF, TNM). x_ Figures 1, 2 D, E

Herbae perennes, erectae; rhizoma repens; caulis 6-45 cm altis; folia late lanceolata-ovata, 6-14 (-25) cm longa et 2.5-6.5 (-11.5) cm lata. Flores masc.: tepala 4, caduca. Flores fem.: tepala 5 vel 6; ovarium 2- vel 0-loculare, abortivum. Chromosoma numero, 2n = 41. Hybrida naturalis e B. aptera et B. formosana.

Erect, perennial, succulent herbs with creeping rhizomes. Rhizomes to 12 mm in diam.; stipules glabrous, widely ovate or triangular, to 8 (-17) mm long, 8 (-15) mm wide, apex apiculate. Stems 6-45 cm tall, to 4 (-12) mm in diam.; cauline stipules glabrous, caducous, ovate, to 13 mm long, 8 mm wide, apex apiculate, margin entire. Leaves sparingly scaberulous on both surfaces, sometimes densely covered by infinitesimal silver-gray spots, broadly lanceolate to obliquely ovate, 6-14 (-25) cm long, 2.5-6.7 (-11.5) cm wide, apex acuminate to apiculate, base obliquely cordate, margins irregularly serrulate or denticulate; venation palmate, veins 7-9; petioles glabrous or sparingly pilose, 1.5-26 (-35) cm long, to 6 mm in diam. Bracts in pairs, papery, glabrous, caducous, lanceolate or ovate, to 8 (-17) mm long, 3 (-12) mm wide, apex mucronate, margins ciliate. Inflorescence at complete development to 5 cm long; peduncles erect to pendulous, to 3 cm long, 1.5 mm in diam. Flowers of both sexes white or pinkish. Staminate flower: tepals 4, decussate, usually unopened, the outer two widely ovate to very widely ovate, 4-9 mm long, 4-10 mm wide, the inner two widely elliptic, 4-8 mm long, 3-6 mm wide; stamens 71-96, golf-club shaped, anthers obovate, 0.8-1.2 mm long, 0.4-0.5 mm across, filaments 0.3-0.5 mm long. Pistillate flower: tepals 5 or 6, unequal, obovate to widely obovate, 12-18 mm long, 6-15 mm wide; styles 2 or 3, yellow, 2.5-3.5 mm long, at their base fused ca. 1.2 mm, each bifid; ovary inferior, ellipsoid, 2-locular, longitudinally shallowly 1- grooved, 3-winged, abaxial wing 5-7 mm long, 5-7 mm wide, lateral wings 1.8-3 mm long, 7-10 mm wide; placenta axile, bilamellate. Abnormal hermaphrodite flowers occasionally seen. Their stamens 1 to several; styles 2 or 2; ovary 2 or 0-locular and 1- or 2 -winged. No fruit production from either pistillate or hermaphrodite flowers. Chromosome number, 2n = 41 (Figure 3).

3Corresponding author. E-mail: bopeng@gate.sinica.edu.tw


Botanical Bulletin of Academia Sinica, Vol. 41, 2000

Figure 1. Begonia taipeiensis. A, Habit; B, Leaf, cross section, showing surface trichomes; C, Inflorescence, showing unopened staminate flowers; D, Inflorescence, showing pistillate flowers; E, Style; F, Stamen; G, Ovary; H, Ovary, cross section, showing placentation. (from Peng 13899, HAST)


Peng and Sue Begonia taipeiensis, hybr. nov. in Taiwan

Additional specimens examined. TAIWAN. Taipei Hsien. Hsichih Town: Paiyunli, at base of a moist mountain slope along Shuiyuan Rd., co-occurring with B. aptera and B. formosana, ca. 210 m alt., 16 Jul 1995, Peng 16320 (HAST). Wulai Hsiang: along trail from Wulai to Hsiaoyi, at mileage sign 16 km on road 9-Alt., which is ca. 2 km from Wulai bus station. Broadleaf forest. Lower part of a rocky slope, on rock face with dripping water, Begonia formosana being abundant along the road. 2450N, 12134E, ca. 200 m alt., 11 Nov 1991, Peng 14804 (HAST); same locality, on seeping rocky slope face. Associated with bryophytes, Selagenella, Alocasia, Rhynchotechum and Thelypteridaceae ferns, ca. 220 m alt., 9 Jul 1992, Peng 15100 (CAS, HAST, TAIF, TNM, OOM); en route from Wulai Station to Hsiaoyi, by Hsiaoyi mountain control station. At mileage sign 18 km on Hsien Rd. 9-A. Broadleaf forest along river. Roadside slope, ca. 300 m alt., 9 Jul 1992, Peng 15105 (HAST); en route from Wulai to Hsiaoyi, mileage sign 5 km, ca. 150 m alt., 27 Jun 1995, Peng 16278

(HAST); en route from Wulai to Hsiaoyi, elev. ca. 270-310 m, 15 Nov 1990, Leu 711 (2 sheets, HAST); en route from Wulai to Hsiaoyi, along Tunghou River. Disturbed broadleaf forest and Cryptomeria plantation, on lower part of a moist cliff, ca. 400-500 m, 11 Jun 1993, Leu 1870 (HAST), Leu 1871 (HAST); From Wulai to Hsioayi, between mileage signs 19 and 20 km on Hsien Rd. 9-Alt., on semi-shady slope beside road, 24 50 54 N, 121 34 53 E, ca. 240 m alt., 17 May 1993, Liu 132 (HAST); en route from Wulai to Hsiaoyi, at mileage sign 16 km on Hsien Rd. 9-A. Beside road, on semishady slope along a small ditch. Herb ca. 25 cm tall; flowers pink-red. 24 50 N, 121 34 E, ca. 200 m alt., 17 May 1993, Liu 133 (HAST).

Distribution and notes. Presently known only in Taipei Hsien, northern Taiwan (Figure 4), scattered for nearly 20 km along a mountain trail on west side of Nanshih River valley at ca. 200-500 m elevation in Wulai. It is also found disjunctly in Hsichih, ca. 25 km northeast of Wulai. Based on a comparison of morphology, distribution pattern, chro

B

C

A


E

D

Figure 2. Photographs of Begonia. A, B. formosana, habit; B, B. formosana, mature and dehiscent capsules; C, B. aptera, habit; D, B. taipeiensis, habit, showing fully open pistillate flowers and precociously dropped staminate flower buds; E, Begonia taipeiensis in cultivation, forming plump capsules with completely shrunken seeds after experimentally backcrossing to putative parents.


Botanical Bulletin of Academia Sinica, Vol. 41, 2000

Figure 3. Microphotographs and camera lucida drawings of chromosome spreads. A-B, B. taipeiensis, 2n = 41, from Peng 14804 (HAST); C-D, B. formosana, n = 30, from Leu 1579 (HAST); E-F, B. aptera, n = 11, fromPeng 14702 (HAST). Bar equals 10 m.


Peng and Sue Begonia taipeiensis, hybr. nov. in Taiwan

mosome cytology and the results of experimental hybridization, we concluded that plants of B. taipeiensis are F1 hybrids between B. aptera Blume [sect. Sphenanthera (Hassk.) Warb.] and B. formosana (Hayata) Masam. [sect. Platycentrum (Klotzsch) A. DC.].

The hybrid nature of B. taipeiensis was initially suspected because of the peculiar flowering habit. As in B. buimontana Yamamoto, a documented natural hybrid in Taiwan (Peng and Chen, 1991), staminate flowers of B.taipeiensis usually develop normally up to the late bud stage and then drop off before they open. Fully open staminate flowers were observed only in one collection, Liu 132 (HAST, see above). Pistillate flowers were always fully open at anthesis, and bud drop did not occur. Fruit set was never observed in the wild. We also found occasional hermaphrodite flowers, which is unusual for Begonia. Plants brought back from the wild and cultivated in the experimental greenhouse behaved similar to plants in nature.

Pollen fertility of B. taipeiensis was estimated by determining the percentage of stainable pollen using malachite green-acid fuchsin-orange G stain of Alexander (1969). Pollen was squeezed out for study from anthers of precociously dropped flower buds of all of the living collections we maintained in the experimental greenhouse of the Institute of Botany, Academia Sinica, Taipei. They revealed nearly complete abortion of the pollen grains. Many grains were aberrant in shape (Figure 5). Cytological studies showed that the meiotic chromosome configurations of B. taipeiensis typically consisted of some sticky, often disoriented bivalents, univalents and multivalent associations (Peng and Chiang, 2000: Figure 2).

Figure 4. Distribution of Begonia aptera (triangles), B. formosana (dots) and Begonia taipeiensis (inset; stars) in Taiwan.

Table 1. Comparison of Begonia taipeiensis with putative parents, B. aptera and B. formosana.

Characters B. aptera B. taipeiensis B. formosana

Creeping rhizome lacking present present

Leaf

Shape lanceolate lanceolate to ovate ovate to very widely ovate Length : width ratio 2.2-4.2 : 1 1.7-2.6 : 1 1.1-2.0 : 1

Pubescence (no./ cm2)

Two-armed glandular trichome 127 26 101 30 108 14

Multiseriate trichome lacking 8 3 11 5

Silver-gray speckles (diam., mm) 0.05-0.25 0.125-0.5 0.625-2.5

flower

Number of ovary cell 3 2 or 0* 2

Number of wings per ovary 0 1*, 2* or 3 3

Number of style 3 2, 2*, 3 2

Number of perianth 6 5-6 5-8

Length of pedicel (mm) 4-6 6-12 12-20

flower

Number of stamens per flower 49-81 71-96 82-124

Inflorescence length (cm) 1.5-5 1-5 6-13

Pollen stainability (%) 78-98 0-1 (-18) 83-100

Chromosome number n = 11 2n = 41 n = 30

Flowering season Jun - Aug Apr - Dec Mar - Dec

*Abnormal, hermaphroditic flower.


Botanical Bulletin of Academia Sinica, Vol. 41, 2000

Figure 5. Aberrant and aborted pollen of Begonia taipeiensis (A) vs. mostly normal and stainable pollen of other species of Begonia, e.g. B. aptera (B). Bar equals 20 m.

Begonia taipeiensis (Figure 2D) was suspected to represent a natural hybrid between B. aptera and B. formosana based on a comparison of morphology and distribution ranges. Begonia aptera (Figure 2C) is a cane-like species (to 110 cm) with lanceolate leaves and clusters of short-peduncled inflorescences drooping from upper leaf axils. Its flowers are pure white and the fruits are fleshy, somewhat berry-like, wingless and 3-loculed. Begonia aptera is common in the northern half of Taiwan at about 50-2,000 melevation. By contrast, B. formosana (Figure 2A) has thick, horizontal rhizomes and ovate to widely ovate

leaves; erect stems are seen during the flowering season. Its inflorescences are long-peduncled and the flowers are white to reddish pink. The fruits are 2-loculed, unequally 3-winged, dry capsules, the abaxial wing protruded prominently (Figure 2B). Begonia formosana is widespread throughout the northern half and eastern part of Taiwan, also at an elevation of. 50-2,000 m. The two species overlap widely geographically and altitudinally. In fact, of the more than 12 species of Begonia in Taiwan, B. aptera and B. fomosana are the only two species distributed in Taipei Hsien, where B. taipeiensis is found. Plants of B. taipeiensis are often found intermixed with or growing near B. aptera and/or B. fomosana. Plants of Begonia taipeiensis are intermediate in many vegetative and floral characters between the putative parents, as shown in Table 1 and Figure 6.

Cytological data are most supportive of the putative parentage of B. taipeiensis. Begonia aptera has n = 11 (Figure 3E-F) and B. formosana has n = 30 (Figure 3C-D) chromosomes (Figure 2) and they have been assigned to different sections of the genus. Begonia taipeiensis has a somatic chromosome number of 2n = 41 (Figure 3A-B), exactly as would be expected in F1 hybrids between the putative parents. In order to substantiate our hypothesis that the new species is derived from natural hybridization between B. aptera and B. formosana, we attempted artificial crosses between them. These trials consistently resulted in germinable seeds and healthy F1 plants, but only when B. formosana was used as the female parent. Molecular data obtained from sequences of the atpB-rbcL spacer of chloroplast DNA also confirmed that unidirectional hybridization between the putative parents in the wild resulted in the formation of B. taipeiensis (Peng and Chiang, 2000). These experimental hybrids closely resembled B. taipeiensis in aspect and morphology. They also shed staminate flowers precociously. Occasionally the staminate flowers opened, but the anther sacs either were empty or contained only a few aborted pollen grains. Ex

Figure 6. Comparison of Begonia taipeiensis with putative parents, B. aptera and B. formosana. A, Leaf; B, Leaf margin; C, Leaf surface trichome; D, Leaf, cross section; E, Ovary, cross section, showing placentation.


Peng and Sue Begonia taipeiensis, hybr. nov. in Taiwan

Flora of Taiwan, Second Edition (eds.), Flora of Taiwan, Second edition, vol. 3. Editorial Committee of the Flora of Taiwan, Second Edition, Taipei, pp. 845-854.

Lai, M.J. 1979. Critical studies on some Begonia from Taiwan. Taiwania 24: 35-37.

Lai, M.J. 1990. Begonia tarokoensis Lai, a new species from eastern Taiwan. Landscape Architect. (Taiwan) 4: 125.

Lai, M.J. and N.J. Chung. 1992. Begonia nantoensis, a new species from Taiwan. Quart.J. Exp. Forest Natl. Taiwan Univ. 1: 59.

Liu, T.S. and M.J. Lai. 1977. Begoniaceae. In H. L. Li, T. S. Liu, T. C. Huang, T. Koyama and C. E. DeVol (eds.) Flora of Taiwan, vol. 3. Epoch Publ. Co., Taipei, pp. 791-798.

Liu, Y.C. and C.H. Ou. 1982. Contributions to the dicotyledonous plants of Taiwan (VII). Bull. Exp. Forest Natl. Chung Hsing Univ. 4: 1-16.

Peng, C.-I and Y.K. Chen. 1990. Begonia austrotaiwanensis (Begoniaceae), a new species from southern Taiwan. J. Arnold Arb. 71: 567-574.

Peng, C.-I and Y.K. Chen. 1991. Hybridity and parentage of Begonia buimontana Yamamoto (Begoniaceae) from Taiwan. Ann. Missouri Bot. Gard. 78: 995-1001.

Peng, C.-I, Y.K. Chen, and H.F. Yen. 1988. Begonia ravenii (Begoniaceae), a new species from Taiwan. Bot. Bull. Acad. Sin. 29: 217-222.

Peng, C.-I and T.Y. Chiang. 2000. Molecular confirmation of unidirectional hybridization in Begonia taipeiensis Peng (Begoniaceae) from Taiwan. Ann. Missouri Bot. Gard. 87: 273-285.

Ying, S.S. 1988. Coloured Illustrated Flora of Taiwan, vol. 3. Published by the author, Taipei, 663 pp.

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perimental backcrossing attempts to putative parents using B. taipeiensis as the ovule donor produced plump capsules (Figure 2E) with completely shrunken seeds.

In conclusion, B. taipeiensis is an F1 hybrid between B. aptera and B. formosana. As a result of discrepancy in chromosome number and/or disharmony in the genomes from the parental species, it is pollen-sterile, sheds staminate flowers prematurely, and fails to set fruit. Although B. taipeiensis is completely sterile, once established, it is able to persist in a given location due to its perennial habit. As in nearly all other congeners, it is also capable of vigorously reproducing from fragments of leaves, stems or rhizomes. Although both parents are widespread and sympatric in the mountainous areas of the northern half of Taiwan, B. taipeiensis is known only from Wulai and Hsichih in the Taipei basin (Figure 4). We believe more intensive and careful field studies will show this natural hybrid to be more abundant than now documented.

Acknowledgements. We thank Drs. David E. Boufford and Thomas G. Lammers for useful comments on the manuscript, Dr. K. N. Gandhi for assistance with the Latin diagnosis, and Mr. Wen-Pen Leu for the handsome line drawing of Begonia taipeiensis. This study was supported in part by research grants from National Science Council (87-2311-B-001-086) and Institute of Botany, Academia Sinica, Taipei to Ching-I Peng.

Literature Cited

Alexander, M.P. 1969. Differential staining of aborted and nonaborted pollen. Stain Techn. 44: 117-122.

Chen, C.H. 1993. Begoniaceae. In Editorial Committee of the


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