Taxus kingstonii

Comparison of holotype of Taxus kingstonii with illustration reproduced from H-l. Li., Woody flora of Taiwan, Fig. 2 (1963).

13. Taxus kingstonii Spjut , J. Bot. Res. Inst. Texas 1(1): 240. 2007.  Type: China. Taiwan: Arisan Prov., Kagi, 2833 m [Mt. Alishan], 2 Feb 1918, tree 25 ft. x 2 ft., only one seen, Wilson 9738, holotype: A! (with male cones; leaf with 10–11 stomata rows/band, abaxial margin with 8 smooth, thick-walled, trapezoidal cells across, anticlinal to periclinal in arrangement, followed by 5 rows of papillose cells, midrib 12 cells wide, mostly smooth, papillose on outer 2 rows); isotypes: BM! (leaf with 13 stomata rows and 9 marginal smooth cells, midrib mostly smooth except upper third of leaf, papillose on outer 2 rows of cells), K! US (p.p.)!

Kingston yew. Forest margins, or summits, 2450-2833 m in Taiwan, to 800 m on mainland Asia; India (Khasi Hills), Myanmar, China (Tibet, Gansu, Shaanxi, Sichuan, Yunnan, Taiwan). 

 Shrub or tree to 12 m high, bole to 65 cm diam; branchlets unequally (type) to equally divided, yellowish green and gradually becoming yellowish with tint of either red, orange or brown; bud scales mostly persistent, 3–4 seriate, turgid, ovate, concave, carinate near apex on upper scales, tan to chestnut brown, lower bud-scales ca. 1.5 mm long. Leaves rigid, spreading usually at less than right angles to branchlets, not parallel to one another, more evenly tapered to base and apex than in T. mairei, lanceolate, narrowly elliptical to oblong (type), or linear in other morphs, evenly tapered to an acute, sharply pointed apex, recurved and/or twisted downwards, 1.5–2.5 cm long, 3.0–3.5 mm wide, 0.35–0.50 mm thick, dark green and convex above to rounded midrib, the adaxial midrib somewhat acute in lower half, often not evident near apex, paler green to yellowish-green and convex below, or plane to concave below to rounded or flush midrib, often with orange tint in the herbarium, or dull rusty brown in the herbarium, thickened and liplike near margins, or plane and slightly revolute near margins; upper (adaxial) epidermal cells in T-sect. wider than tall, nearly wide rectangular or ellipitical in T-sect., usually 20–25 um tall and 25–30 um wide, thin-walled, slightly inflated; lower (abaxial) epidermal cells similar in T-sect. but not as large, 15–25 um tall, 20–30 um wide, slightly inflated near margin in 2–5 rows, more nearly rectangular in 7–11 cell rows near stomata bands, usually relatively short on midrib, 1–4 (-10)× l/w, sharply 4–6 angled, often wider and more slanted at one end (trapezoidal), not inflated (in T-sect) as in T. mairei, papillose to ca. (7-) 8–12 (-19) rows of cells from margins, typically without papillae on midrib (except young leaves), or partially papillose on outer midrib; papillae submarginal to medial in 2–3 irregular rows across each cell. Stomata bands broader than the non-stomatal region, olive green in fresh material; yellowish orange in dried leaves; stomata continuous in 11–15 rows, separated by 1–2 rows of accessory cells, stoma often with a blackish halo. Male cone scales generally 4-seriate, globose, ca. 4 mm diam, yellowish-green, pollen sacs mostly 6, pale pink with reddish mid region and patchy resinous areas. Female cone in bud subcylindric, ca. 2 mm long, greenish, scales mostly 5-seriate, conduplicate at base, maturing on 1st yr branchlets; seeds ovoid, dull, tan or purplish, stained by aril, angular where tapering to apex, or not angled, to 7 mm long, 4 mm wide.

     Taxus kingstonii is recognized by the relatively turgid recurved leaves (twist and curve downwards along their blades) that taper rather evenly to apex, and by the rusty orange color on the abaxial leaf surface (dried specimens).  In herbarium specimens, the leaves often crisscross, especially near apex of branchlets, whereas leaves in other species of the Sumatrana Group—that are reddish or greenish in color—appear more evenly two-ranked and tightly adpressed to branchlets.  These differences seem related to the manner in which leaves twist, which may also correlate with leaf shape as seen by the evenly tapered leaf in the Kingston yew compared to the falcate leaf in other species (indented more along lower margin near petiole; Fig. 20, 21, 30, 31).

     Other features that help distinguish the Kingston yew are seen on the abaxial leaf midrib (note: 27 June  2006—as seen mostly from specimens from Khasia, Tibet, Gansu, Sichuan, and Taiwan, but not in some specimens from Yunnan).  It usually forms a rounded keel, in contrast to a truncated ridge that may either be flush with the surface in T. celebica, or elevated in T. mairei.  Its epidermal cells are short trapezoidal to almost rectangular, and in T-section appear similar in size and shape to those on the adaxial surface, or the adaxial cells sometimes are larger and nearly isodiametric.  Taxus mairei, on the other hand, has shorter trapezoidal cells on its abaxial midrib, but in T-section they appear larger and nearly globose—in contrast with the shorter elliptical cells on the adaxial surface.  The abaxial midribs of the related T. sumatrana and T. celebica have longer, nearly rectangular cells that in T-section are similar in size on both surfaces.

     The Kingston yew also has conspicuous persistent bud-scales at the base of young branchlets, in contrast to those of related species in the Sumatrana Group that appear vestigial as in T. chinensis.  

     The Kingston yew generally occurs at elevations between that of T. mairei (below 1200 m) and that of T. wallichiana (above 2300 m).  Variation ascribed to T. kingstonii may include hybrids with T. chinensis and T. mairei in Shaanzi, Gansu and Sichuan, T. celebica in Yunnan and Burma, and T. wallichiana in NE India.  These alleged hybrids, however, show disjunct geographical relationships as further described in the examples that follow.

     (A) Four collections, two from Shaanxi, one from Gansu, and another from Sichuan that I had annotated T. chinensis without microscopic examination of leaves, were later found to lack papillae on the abaxial midrib, a feature that I employ to distinguish T. chinensis from T. kingstonii.  Their leaves spread nearly at right angles—parallel to each other—and have the greenish color of T. chinensis; otherwise, they compare favorably with typical T. kingstonii.  The close morphological similarity among these specimens, along with their more northern geographical occurrence, suggests a distinct taxon.

      (B) Two collections, one from Taiwan (Liu et al. 389) and one from Yunnan (Forrest 12087), resemble T. mairei by the isodichotomous branching, leaves spreading at right angles, and by the thin-walled leaf epidermal cells with a yellowish chloroplast, but are regarded T. kingstonii by the rusty orange color on leaves and branchlets, and by the leaves ± evenly tapered to base and apex.  The abaxial leaf epidermal cells in the specimen from Yunnan are not enlarged on the midrib—further supporting its determination as T. kingstonii, whereas the Taiwan specimen has slightly larger cells—indicating that it could be assigned to T. mairei.  Yet, the closer similarity between these specimens than to other specimens indicates a common but distinct ancestry.

      (C) Collections from Yunnan (Forrest 11789, 15945, Forrest s.n. A), Khasia (Hooker 77 P, Hooker 137 P, Hooker & Thomson s.n. yr 1855 P) and from Taiwan (C-j. Chang 1–6, without specific locality) resemble T. celebica or T. sumatrana by the acuminate tapered leaf but are referred to T. kingstonii by the leaves spreading obliquely (Fig. 18), tapering evenly to base, having a uniformly rusty orange color on the abaxial surface, and having short trapezoidal epidermal cells on the abaxial midrib that in T-section are not larger than those on the adaxial surface.  On one hand, these specimens have much in common to indicate they belong to a distinct taxon while on the other hand specimens from Khasia (Mann s.n. P, Fig. 19) appear intermediate to T. wallichiana by the thicker glossy leaves, or belong to T. sumatrana, distinguished by the thinner puckered leaves (Mann s.n., “10 ft high”—annotated Cephalotaxus mannii, GH, Taxus baccata, A).  The Yunnan specimens have relatively thin leaves, a character trait that may have been acquired by hybridization with T. celebica (or T. sumatrana).  Thus, the Yunnan and Khasia plants of the Kingston yew could also be polyphyletic.

      The shape of the leaf epidermal cells on the abaxial surface also helps separate T. kingstonii from the T. chinensis species complex (T. aff. chinensis in Appendix; T. phytonii Spjut ined.; T. phytonii var. obscura Spjut ined, in adnot. A, GH, K, P, U), particularly T. obscura ined. as defined in the preceding key.  Specimens of this species complex from Luzon and Taiwan are remarkably similar to T. kingstonii in their leaf characteristics of color and arrangement, but differ in more papillose cells on midrib and marginal zones—occurring to within (8-) 4 (-2) cells from the margins.  Occasional specimens from Luzon (Sulit 2350, Alvarey 18369 from Benquet Mt.), Fujian (Chung 3866) and Thailand (Lobb 461) with fewer papillose cells—lacking across 8 marginal cells and often on the lower half of the midrib—may be hybrids between T. obscura (ined.) and T. kingstonii. They were identified T. kingstonii in my 1996 annotations, but considered T. obscura (ined.) in this paper by the fusiform shape of the epidermal cells on the abaxial surface of leaves.

     On the other hand a more conservative treatment might include the Philippine yews (T. obscura ined.) under T. kingstonii based on leaf arrangement and color, a character that I had applied to a limited extent that resulted in other Philippine specimens being included under T. kingstonii in my 1996 annotations (e.g., Leano 25128).  This, however, seems contrary to leaf anatomical data in this study.  The relatively narrow border of bare marginal cells (4 cells wide), the papillose midrib, and the 11–14 stomata rows/band occur consistently in many specimens that would seem to merit separate taxonomic status.  It is also interesting that Ludlow & Sherriff 3719 from NE India has similarly discolored leaf surfaces with elliptical shaped epidermal cells in T-section, 12 stomata rows/band, and a papillose undersurface that extends entirely across the reddish marginal zone, and that Tsai 59874 from Yunnan, and that Neth. Ind. For. Serv. bb:20887 from Sulawesi, are also similar in this regard. Their leaf characteristics compare more with The Philippines yews than with those in the Himalayas.  Further study is needed to determine to what extent epidermal papillae are influenced by genetic and environmental factors.

     Taxus kingstonii is named in honor of David G. I. Kingston, a chemist who has done extensive work on elucidating and summarizing the taxane chemistry of the genus (e.g., Kingston 1996; Kingston et al. 1990.  Taxol, from which the drug paclitaxel is marketed and used to treat ovarian and other cancers, was originally isolated from dried bark of T. brevifolia; however, fresh leaves of many species of Taxus have proved suitable for obtaining taxanes.  Taxol was first characterized by Monroe Wall’s group (Research Triangle Institute, Wani et al. 1971).  They also discovered other significant antitumor agents such as camptothecin and holacanthone (Wall et al. 1972).

Representative Specimens—India: Khasia, Hooker L77 (PH), 1337 (K) Simmons 484 (P), Nungluai, 5000 ft, Mann (K, P). Myanmar: Bernardmyo, Ruby Mines, 5600 ft (K). China—Tibet: Oriental, Haut Mekong, Tsekou to Nekou, Soulie1411 (P: 2 sheets). Gansu: F. N. Meyer 1790 ex USDA (P). Shaanxi (Shensi) Davis 1872 (P). Tsin-lin au  Lao-lin, 3000 m.  Sichuan: Tachienlu Cheng 1001 (BM), Cheng 1475 (P). Yunnan: Shweli-Salween Divide, 10,000 ft, 25º20 N, shrub 10–20 ft, open shady thickets, Forrest 11789 (BM, K), Salween, Forrest 12087 (K, S: C-2093), Forrest s.n. (A); Ma-Chang-Kai, valley, 25º30 N, 6000 ft., shrub, 20–30 ft., in thickets, Dec 1918, Forrest 9462 (A, K), Forrest 15945 (BM, K); Salween E of Tengyueh, to summit of Shwell, Shwelli River, Rock 7587 (US).  Taiwan: Paseian San [Pahsienshan], Hsi 165 (PH); Fig. 3 in Li, Woody Fl. Taiwan, Liu et al. 437, (M, T, US); Mt. Ammachan, Liu 0389 (A, K), Arizan, Nitak (PH); Mt. Ammashan, Taichung Hsien, C.C. Tseng s.n. (BH); Tongshi, C-j. Chang, Dongshi #2, Tongshi #6, without locality data, 4 Mar 1993 (wba).

Gansu: F. N. Meyer 1790 ex USDA (P).  This specimen was examined under light microscope at the Museum of Natural History in Paris (P) and the abaxial leaf midrib appeared papillose; thus, the annotation label for T. chinensis was provided.  However, upon later study of a leaf fragment under higher magnification, no papillae were seen on midrib cells.  It is felt that the presence of papillae on the abaxial midrib observed in so many specimens of T. chinensis from central China has taxonomic significance.  Also, most specimens of T. chinensis have yellowish-green branchlets with grayish bud-scale scars.  The type for T. kingstonii from Taiwan has leaves similar in texture and shape to T. chinensis, but are more tapered near base and do not spread as wide from branchlets. The rusty orange color and the absence of midrib papillae are given taxonomic weight to the determination for T. kingstonii.  Further study may prove that this and other variations assigned to T. kingstonii are worthy of distinct varieties.

Sichuan: Tachienlu Cheng 1001 (BM).  Three taxonomists had independently determined the specimen on the left to be T. chinensis; however, leaf anatomical features do not confirm this (illustration).  The rusty orange tint on branchlets support the new determination of T. kingstonii.  The photos to the right of the illustration are from the same area collected by Cheng (1475, P).  The seed has a short nipple at apex.

Yunnan: Salween E of Tengyueh, to summit of Shwell, Shwelli River, Rock 7587 (US).  This specimen  has a distinct adaxial leaf surface. The branchlets have a rusty orange tint.  A leaf examined under the microscope was found to have a relatively narrow margin of cells, 9 cells across.   The abaxial midrib cells were irregularly widened and lacked papillae.  These features best agree with T. kingstonii.

China—Tibet: Oriental, Haut Mekong, Tsekou to Nekou, Soulie1411 (P: 2 sheets).

China—Taiwan: C-j. Chang,
Tongshi No. 6, 26 Nov. 1993

Note that leaves on the adaxial surface are strongly convex in contrast to a more level surface in T. mairei.

China—Taiwan: C-j. Chang,
Tongshi No. 6, 13 Jan. 1994

China—Taiwan: C-j. Chang,
3 of 6, 4 Mar 1993.  Identified in 1993 as T. kingstonii
  by the thickened leaf margins and by leaf midrib
on the abaxial surface forming an elevated round
keel.  Image scanned 1 June 2007.  Leaves now appear reddish orange along margins and on midrib.
 Leaf arrangement and shape are intermediate
to T. mairei.  Leaves generally have 6–10 marginal cells without papillae followed by (6–) 8 (-10) rows of papillose cells, a stomata band with 11–13 rows of stomata.  Abaxial midrib was commonly 13 cells wide with papillae on the outer 2–3 rows of cells.  In the close-up photos, one can actually see and count the stomata rows.

References: see Introduction to Taxus, Overview of the genus Taxus, and Spjut 2007a, 2007b.

Spjut, R. W. 2007a. A phytogeographical analysis of Taxus (Taxaceae) based on leaf anatomical characters.  J. Bot. Res. Inst. Texas 1(1): 291–332

Spjut, R. W. 2007b. Taxonomy and nomenclature of Taxus.  J. Bot. Res. Inst. Texas 1(1): 203–289.